Misplaced Pages

#852147

71-479: Body composition models typically use between 2 and 6 compartments to describe the body. Common models include: As a rule, the compartments must sum to the body weight. The proportion of each compartment as a percent is often reported, found by dividing the compartment weight by the body weight. Individual compartments may be estimated based on population averages or measured directly or indirectly. Many measurement methods exist with varying levels of accuracy. Typically,

142-419: A capacitive linear encoder . Inexpensive Chinese models have 56 narrow emitter plates and one long receiver plate etched on the sliding display's printed circuit board , which intersect with a repeating pattern of T-shaped plates in the longer "stator" board. The top of the "T" plates intersect with the receiver plate, while the vertical bars of each "T" intersect with the emitter plates. The pitch of each "T" in

213-542: A magnifying glass to read and can be difficult to read from a distance or from awkward angles. It is relatively easy to misread the last digit. In production environments, reading vernier calipers all day long is error-prone and is annoying to the workers. Dial calipers are comparatively easy to read, especially when seeking the exact center by rocking and observing the needle movement. They can be set to 0 at any point for comparisons. They are usually fairly susceptible to shock damage. They are also very prone to getting dirt in

284-509: A micrometer caliper or, more often, simply a micrometer . (Sometimes the term caliper , referring to any other type in this article, is held in contradistinction to micrometer .) Each of the above types of calipers has its relative merits and faults. Vernier calipers are rugged and have long-lasting accuracy, are coolant proof, are not affected by magnetic fields, and are largely shockproof. They may have both centimeter and inch scales. However, vernier calipers require good eyesight or

355-438: A plural only ( plurale tantum ) form, like scissors or glasses . Colloquially, the phrase "pair of verniers" or just "vernier" might refer to a vernier caliper. In loose colloquial usage, these phrases may also refer to other kinds of calipers, although they involve no vernier scale. In machine-shop usage, the term "caliper" is often used in contradistinction to micrometer , even though outside micrometers are technically

426-413: A scale drawn on the map. On a nautical chart the distance is often measured on the latitude scale appearing on the sides of the map: one minute of arc along any great circle , e.g. any longitude meridian, is approximately one nautical mile or 1852 meters . Dividers are also used in the medical profession. An ECG (also EKG) caliper transfers distance on an electrocardiogram ; in conjunction with

497-417: A base that extends their usefulness as a depth gauge and a jaw attachment that all allows measuring the center distance between holes. Since the 1970s, a clever modification of the moveable jaw on the back side of any caliper allows for step or depth measurements in addition to external caliper measurements, similarly to a universal micrometer (e.g., Starrett Mul-T-Anvil or Mitutoyo Uni-Mike). The method to use

568-447: A caliper is highly dependent on the skill of the operator. Regardless of type, a caliper's jaws must be forced into contact with the part being measured. As both part and caliper are always to some extent elastic , the amount of force used affects the indication. A consistent, firm touch is correct. Too much force results in an under indication as part and tool distort; too little force gives insufficient contact and an over indication. This

639-405: A corrupt form of caliber . Many types of calipers permit reading out a measurement on a ruled scale , a dial , or an electronic digital display . A common association is to calipers using a sliding vernier scale . Some calipers can be as simple as a compass with inward or outward-facing points, but with no scale (measurement indication). The tips of the caliper are adjusted to fit across

710-414: A definition. When referring to this meaning, gold standard tests are normally not performed at all. This is because the gold standard test may be difficult to perform or may be impossible to perform on a living person (i.e. the test is performed as part of an autopsy or may take too long for the results of the test to be available to be clinically useful). Other times, the "gold standard" does not refer to

781-428: A digital recorder, spreadsheet , statistical process control program, or similar software on a personal computer . Interfacing devices based on RS-232 , Universal Serial Bus , or wireless can be built or purchased. The serial digital output varies among manufacturers, but common options are: A caliper using a calibrated screw for measurement, rather than a slide, is called an external micrometer caliper gauge ,

SECTION 10

#1732890886853

852-471: A female thirty year old will have a different ideal fat percentage than a male thirty year old. An athlete will have a different ideal than a non athlete, and it can depend on the sport. The physical activities which can help decrease fat mass, increase lean mass, or both are the same for everybody. Aerobic exercise, also known as cardio (heart) exercise, decreases fat. High intensity interval training (HIIT) in particular helps decrease visceral fat. Visceral fat

923-561: A form of caliper. In this usage, caliper implies only the form factor of the instrument. The earliest caliper has been found in the Greek Giglio wreck near the Italian coast. The ship's find dates to the 6th century BC. The wooden piece already featured a fixed and a movable jaw. Although rare finds, calipers remained in use by the Greeks and Romans . A bronze caliper, dating from 9 AD,

994-449: A line parallel to the edge. In the diagram at left, the uppermost caliper has a slight shoulder in the bent leg allowing it to sit on the edge more securely. The lower caliper lacks this feature but has a renewable scriber that can be adjusted for wear, as well as being replaced when excessively worn. The labelled parts are The calipers in the diagram show a primary reading on the metric scale of about 2.475 cm (2.4 cm read from

1065-474: A magnetic field to the body and measures the difference in relaxation rates of hydrogen atoms within fat versus lean mass. It functions similarly to magnetic resonance imaging (MRI) but instead of providing an image like MRI, QMR gives quantities of fat mass, lean mass, and total body water. QMR is also widely used for body composition analysis of animals, including laboratory animals like mice, and wildlife including birds. Assessment of somatic (skeletal) protein

1136-413: A master object and subsequently being able to read directly the plus-or-minus variance in the size of subsequent objects relative to the master object). The slide of a dial caliper can usually be locked at a setting using a small lever or screw; this allows simple go/no-go checks of part sizes. Rather than a rack and pinion , digital calipers use a linear encoder . A liquid-crystal display shows

1207-447: A precision to 0.01 mm (10 micrometres ), or one thousandth of an inch. They are available in sizes that can measure up to 1828 mm (72 in). Instead of using a vernier mechanism, which requires some practice to use, the dial caliper reads the final fraction of a millimeter or inch on a simple dial. In this instrument, a small, precise rack and pinion drives a pointer on a circular dial , allowing direct reading without

1278-409: A probe that is attached to the movable head and slides along the centre of the body. This probe is slender and can get into deep grooves that may prove difficult for other measuring tools. The vernier scales may include metric measurements on the lower part of the scale and inch measurements on the upper, or vice versa, in countries that use inches. Vernier calipers commonly used in industry provide

1349-511: A resolution of 0.01 mm or 0.0005 in, but accuracy may not be better than about ±0.02 mm or 0.001 in for 150 mm (6 in) calipers, and worse for longer ones. A caliper must be properly applied against the part in order to take the desired measurement. For example, when measuring the thickness of a plate, a vernier caliper must be held at right angles to the piece. Some practice may be needed to measure round or irregular objects correctly. Accuracy of measurement when using

1420-412: A test becomes popular and is declared to be the gold standard without adequate consideration of alternatives or despite weaknesses. As new diagnostic methods become available, the "gold standard" test may change over time. For instance, for the diagnosis of aortic dissection , the gold standard test used to be the aortogram , which had a sensitivity as low as 83% and a specificity as low as 87%. Since

1491-411: A vernier scale or caliper with zero error is to use the formula "actual reading = main scale + vernier scale − (zero error)". Zero error may arise due to knocks that affect the calibration at 0.00 mm when the jaws are perfectly closed or just touching each other. Positive zero error refers to the fact that when the jaws of the vernier caliper are just closed, the reading is a positive reading away from

SECTION 20

#1732890886853

1562-436: Is bioelectrical impedance analysis (BIA), which uses the resistance of electrical flow through the body. BIA is highly sensitive to hydration status and water intake. Drinking water dilutes the electrolytes in the body, making it less conductive, as does increasing body fat. By controlling hydration status or performing multiple impedance measurements, it is possible to estimate body fat and other variables. InBody developed

1633-402: Is a direct application of Archimedes' principle, that an object displaces its own volume of water. Air displacement plethysmography is an alternative to underwater weighing for measuring body volume. The technique uses air as opposed to water and is known as air displacement plethysmography (ADP). Subjects enter a sealed chamber that measures their body volume through the displacement of air in

1704-433: Is a greater problem with a caliper incorporating a wheel, which lends mechanical advantage . This is especially the case with digital calipers, calipers out of adjustment, or calipers with a poor quality beam. Simple calipers are uncalibrated; the measurement taken must be compared against a scale. Whether the scale is part of the caliper or not, all analog calipers—verniers and dials—require good eyesight in order to achieve

1775-420: Is a naturally occurring radioactive isotope found in intracellular water, but is not present in stored triglycerides (fat). Whole body counting can measure the amount of potassium 40 (40K) in the body, a quantity called total body potassium (TBK). This can be used to estimate fat-free mass directly. It has mostly been replaced by newer, more accurate techniques such as DEXA. Another method to estimate body water

1846-485: Is a technique used for measuring body shape. Initially, BVI technology employed white light scanning machines to measure an individual's body shape. However, recent technological advances in 3D measurement have enabled BVI to be calculated using images taken on a smartphone. Two images are required to create an individual 3D silhouette. By comparing this 3D silhouette with MRI data, body volume and fat distribution can be calculated. Body composition can also be measured using

1917-458: Is assumed to be the ground truth. Some authors use the term "golden standard". Claassen argues this usage is incorrect, as "golden standard" implies a level of perfection that is unattainable in medical science. Caliper Caliper(s) or calliper(s) are an instrument used to measure the linear dimensions of an object or hole; namely, the length , width, thickness, diameter or depth of an object or hole. The word "caliper" comes from

1988-400: Is especially important when a perfect test is available only by autopsy. A test has to meet some interobserver agreement, to avoid some bias induced by the study itself. Calibration errors can lead to misdiagnosis . Sometimes "gold standard test" refers to the best-performing test available. In these cases, there is no other criterion against which it can be compared and it is equivalent to

2059-529: Is near the internal organs, while subcutaneous fat is just under the skin. The former is more tightly associated with poor metabolic health. Bone and muscle strengthening exercise, also known as resistant training, decreases fat mass and increases lean mass at the same time, though it does better at the latter. In order to prevent injury from repetitive motion, people should do resistant training with different parts of their bodies on different days. Gold standard (test) In medicine and medical statistics ,

2130-445: Is typically determined by simple measurements and calculations, including mid-arm circumference (MAC), mid-arm muscle circumference (MAMC), and creatinine height ratio (CHI). Creatinine height ratio is calculated as 24-hour urine creatinine multiplied by 100 over the expected 24-hour urine creatinine for height. This calculation results in a percentage that can indicate protein depletion. Many methods of determining body composition use

2201-468: The Archives of Biological Medicine and Rehabilitation specifies this usage. In practice, however, the uptake of this term by authors, as well as enforcement by editorial staff, is notably poor, at least for AMA journals. When the criterion is a whole clinical testing procedure it is usually referred to as clinical case definition . Differing case definitions can produce wildly different results when used as

Body composition - Misplaced Pages Continue

2272-457: The body weight as a measurement, determined via a weighing scale . Other details such as height and age can be correlated with other measures and are often used in estimation formulas. The methods above are each valid and notable in providing a measurement that can be used to determine the "true body composition" of the tested individual. However, each method does possess its own individual limitations, such as accuracy, precision, or expense, and

2343-408: The full width of the smallest interval on the vernier scale (0.005 cm). Assuming no systematics affect the measurement (the instrument works perfectly), a complete measurement would then read 2.462 cm ± 0.005 cm. The vernier, dial, and digital calipers directly read the distance measured with high accuracy and precision . They are functionally identical, with different ways of reading

2414-498: The gold standard , criterion standard , or reference standard is the diagnostic test or benchmark that is the best available under reasonable conditions. It is the test against which new tests are compared to gauge their validity, and it is used to evaluate the efficacy of treatments. The meaning of "gold standard" may differ between practical medicine and the statistical ideal. With some medical conditions, only an autopsy can guarantee diagnostic certainty. In these cases,

2485-479: The "gold standard" test of a medication or procedure is whether or not it leads to an increase in the number of neurologically intact survivors that walk out of the hospital. Other types of medical research might regard a significant decrease in 30-day mortality as the gold standard. The AMA Style Guide has preferred the phrase criterion standard instead of "gold standard." Other journals have also issued mandates in their instructions for contributors. For instance,

2556-500: The 4-compartment model consists of a weight measurement, body density measurement using hydrostatic weighing or air displacement plethysmography , total body water calculation using isotope dilution analysis, and mineral content measurement by dual-energy X-ray absorptiometry (DEXA). However, it is also common to use a DEXA scan alone and refer to this as the "gold standard". These claims are somewhat dubious since measurements methods vary significantly from study to study. In practice,

2627-410: The accuracy of BIA machines. BIA machines have found acceptance in medical, fitness, and wellness space owing to their ease-of-use, portability, quick measurements, and cost efficiency. AURA Devices developed and launched a number of wearable bioimpedance trackers, including the first smart strap for Apple Watch that tracks body fat, muscles, lean mass, water levels, etc. The Body Volume Index (BVI)

2698-423: The actual reading of 0.00 mm. If the reading is 0.10 mm, the zero error is referred to as +0.10 mm. Negative zero error refers to the fact that when the jaws of the vernier caliper are just closed, the reading is a negative reading away from the actual reading of 0.00 mm. If the reading is −0.08 mm, the zero error is referred to as −0.08 mm. Calipers with measurement axes displaced from

2769-430: The advancements of magnetic resonance imaging , the magnetic resonance angiogram (MRA) has become the new gold standard test for aortic dissection, with a sensitivity of 95% and a specificity of 92%. Before the widespread acceptance of any new test, the former test retains its status as the "gold standard". Because tests can be incorrect (yielding a false-negative or a false-positive ), results should be interpreted in

2840-422: The advantage of being able to also directly measure muscle thickness and quantify intramuscular fat. In the abdomen, ultrasonography is a useful tool for quantifying both subcutaneous and visceral fat. Ultrasonography has many advantages over CT scan and MRI as it is non-invasive and doesn't utilize ionizing radiation, making it more accessible to special populations. Quantitative magnetic resonance (QMR) applies

2911-434: The appropriate scale, the heart rate can be determined. A pocket caliper version was invented by cardiologist Robert A. Mackin. Oddleg calipers , Hermaphrodite calipers , or Oddleg Jennys , as pictured on the left, are generally used to scribe a line at a set distance from the edge of a workpiece. The bent leg is used to run along the workpiece edge while the scriber makes its mark at a predetermined distance, this ensures

Body composition - Misplaced Pages Continue

2982-509: The basis for evalulating a given diagnostic method. A hypothetical ideal "gold standard" test has a sensitivity of 100% concerning the presence of the disease (it identifies all individuals with a well-defined disease process; it does not have any false-negative results) and a specificity of 100% (it does not falsely identify someone with a condition that does not have the condition; it does not have any false-positive results). In practice, there are no true gold standard tests. Sometimes

3053-403: The best-performing test available, but the best available under reasonable conditions. For example, in this sense, an MRI is the gold standard for brain tumor diagnosis, though it is not as good as a biopsy. In this case, the sensitivity and specificity of the gold standard are not 100% and it is said to be an "imperfect gold standard" or "alloyed gold standard". The term ground truth refers to

3124-443: The calipers are used to measure a large diameter pipe. A vernier caliper does not have the depth capacity to straddle this large diameter and at the same time reach the outermost points of the pipe's diameter. They are made from high carbon steel. In the metalworking field, a divider caliper, popularly called a compass, is used to mark out locations. The points are sharpened so that they act as scribers; one leg can then be placed in

3195-424: The chamber. Next, body volume is combined with body weight (mass) to determine body density. The technique then estimates the percentage of body fat and lean body mass (LBM) through empirically derived equations similar to those used with underwater weighing (for the density of fat and fat-free mass). Total body water may be effectively measured using isotope dilution analysis of deuterium oxide. Potassium 40

3266-425: The combination of methods also has limitations. Often, the relative change from one period to the next is most important; if an individual can maintain all factors as similar as possible, even a simple method such as weighing may give enough information to determine the true change in composition. The ideal percent of body mass which should be fat depends on an individual's sex, age, and physical activity. For example,

3337-400: The context of the history, physical findings, and other test results of the individual being tested. It is within this context that the sensitivity and specificity of the "gold standard" test is determined. When the gold standard is not a perfect one, its sensitivity and specificity must be calibrated against more accurate tests or against the definition of the condition. This calibration

3408-403: The dimple created by a center or prick punch and the other leg pivoted so that it scribes a line on the workpiece's surface, thus forming an arc or circle. Their namesake use is in dividing a workpiece of arbitrary width into equal-width sections: by "walking" the tool from one end to the other by pivoting it from one point to the next until reaching the other end, then adjusting the gap between

3479-417: The error on the measurement is also important. Ignoring the possibility of interpolation by eye, both the primary reading and the zero point reading are bounded by plus/minus half the length corresponding to the width of the smallest interval on the vernier scale (0.0025 cm). These are "absolute" errors and absolute errors add, so the length reading is then bounded by plus/minus the length corresponding to

3550-598: The gears, which can cause accuracy problems. Digital calipers switch easily between centimeter and inch systems. They can be set to zero easily at any point with a full count in either direction and can take measurements even if the display is completely hidden, either by using a "hold" key, or by zeroing the display and closing the jaws, showing the correct measurement, but negative. They can be mechanically and electronically fragile. Most also require batteries and do not resist coolant well. They are also only moderately shockproof and can be vulnerable to dirt. Calipers may read to

3621-443: The gold standard test is the best test that keeps the patient alive, and even gold standard tests can require follow-up to confirm or refute the diagnosis. The term 'gold standard' in its current sense in medical research was coined by Rudd in 1979, in reference to the monetary gold standard. "Gold standard" can refer to popular clinical endpoints by which scientific evidence is evaluated. For example, in resuscitation research,

SECTION 50

#1732890886853

3692-423: The higher compartment models are more accurate, as they require more data and thus account for more variation across individuals. The four compartment model is considered the reference model for assessment of body composition as it is robust to most variation and each of its components can be measured directly. A wide variety of body composition measurement methods exist. The gold standard measurement technique for

3763-628: The highest precision. Digital calipers have an advantage in this area. Calibrated calipers may be mishandled, leading to loss of zero . When a caliper's jaws are fully closed, it should, of course, indicate zero. If it does not, it must be recalibrated or repaired. A vernier caliper does not easily lose its calibration, but a sharp impact or accidental damage to the measuring surface in the caliper jaw can be significant enough to displace zero. Digital calipers have zero set buttons, for quick recalibration. Vernier, dial and digital calipers can be used with accessories that extend their usefulness. Examples are

3834-410: The internal size of an object. Outside calipers are used to measure the external size of an object. The same observations and technique apply to this type of caliper, as for the inside caliper. With some understanding of their limitations and usage, these instruments can provide a high degree of accuracy and repeatability. They are especially useful when measuring over very large distances; consider if

3905-417: The main scale plus about 0.075 cm from the vernier scale). Calipers often have a "zero point error": meaning that the calipers do not read 0.000 cm when the jaws are closed. The zero point error must always be subtracted from the primary reading. Let us assume these calipers have a zero-point error of 0.013 cm. This would give us a length reading of 2.462 cm. For any measurement, reporting

3976-572: The measurement methods used will be a tradeoff between cost, availability, and accuracy. Body composition measurement with dual energy X-ray absorptiometry (DEXA) is used increasingly for a variety of clinical and research applications. A DEXA scan requires medical supervision by a radiologist. Total body scans using DEXA give accurate and precise measurements of body composition, including bone mineral content (BMC), bone mineral density (BMD), lean tissue mass, fat tissue mass, and fractional contribution of fat. DEXA measurements are highly reproducible if

4047-424: The measurement, which often can switch units between millimeters and fractional or decimal inches. All provide for zeroing the display at any point along the slide, allowing the same sort of differential measurements as with the dial caliper. Digital calipers may contain a "reading hold" feature, allowing the reading of dimensions after use in awkward locations where the display cannot be seen. Like analog calipers,

4118-412: The need to read a vernier scale. Typically, the pointer rotates once every inch, tenth of an inch, or 1 millimeter. This measurement must be added to the coarse whole inches or centimeters read from the slide. The dial is usually arranged to be rotatable beneath the pointer, allowing for "differential" measurements (the measuring of the difference in size between two objects, or the setting of the dial using

4189-566: The period), each connected to 7 emitter plates, and the resulting analog signal is read through a single receiver plate. The 1983 German patent DE3340782C2 (see figure) is said to describe the workings. Other digital calipers contain an inductive linear encoder, which allows robust performance in the presence of contamination such as coolants. Magnetic linear encoders are used in yet other digital calipers. Digital calipers nowadays offer serial data output to expedite repeated measurements, avoid human error , and allow direct data entry into

4260-518: The points to be measured, and then kept at that span while moved to separate measuring device, such as a ruler . Calipers are used in many fields such as mechanical engineering , metalworking , forestry , woodworking , science and medicine . Caliper is the American spelling , while calliper (double "L") is the British spelling. A single tool might be referred to as a caliper or as calipers —

4331-425: The points until the "walk" ends directly on the end point, equal divisions can be easily marked out without any measuring. A divider caliper is also used to measure a distance between two points on a map. The two caliper ends are brought to the two points whose distance is being measured. The caliper's opening is then either measured on a separate ruler and then converted to the actual distance, or measured directly on

SECTION 60

#1732890886853

4402-401: The reading. This would be a simply calibrated caliper, but the addition of a vernier scale allows more accurate interpolation and is the universal practice; this is the vernier caliper . Vernier, dial, and digital calipers can measure internal dimensions (using the uppermost jaws in the picture at right), external dimensions using the pictured lower jaws, and in many cases depth by the use of

4473-406: The result. These calipers comprise a calibrated scale with a fixed jaw, and another jaw, with a pointer, that slides along the scale. The distance between the jaws is then read in different ways for the three types. The simplest method is to read the position of the pointer directly on the scale. When the pointer is between two markings, the user can mentally interpolate to improve the precision of

4544-454: The role of DEXA in clinical evaluations and research studies has been questioned by Wang et al. who stated that "the errors of the DXA [DEXA] method are still of concern if it were to be used as the criterion." Hydrostatic weighing, also referred to as underwater weighing, hydrostatic body composition analysis and hydrodensitometry, is a technique for measuring the density of a living person's body. It

4615-458: The same type of machine is used, making them excellent for monitoring pharmaceutical therapy, nutritional or exercise intervention, sports training, and other body composition altering programs. They are also fast, simple, non-invasive, and expose the subject to a level of x-rays less than that of a cross-country flight. DEXA exams provide both total body and up to 14 regional (trunk, individual arms & legs, android, gynoid, etc.) results. However,

4686-549: The skin fold test, which is performed using a measuring caliper . It can be done in nine steps: A common skin fold method is by using gun style calipers to measure the thickness of subcutaneous fat in multiple places on the body. This includes the abdominal area, the subscapular region, arms, buttocks and thighs. These measurements are then used to estimate total body fat. Ultrasound has also been used to measure subcutaneous fat thickness, and by using multiple points an estimation of body composition can be made. Ultrasound has

4757-513: The slide of many digital calipers can be locked using a lever or screw. Ordinary 150 mm (6  in ) digital calipers made of stainless steel have a rated accuracy of 0.02 mm ( 0.001 in ) and a resolution of 0.01 mm (0.0005 in). The same technology is used for longer calipers, but accuracy declines to 0.03 mm (0.001 in) for 100–200 mm (4–8 in) and 0.04 mm (0.0015 in) for 200–300 mm (8–12 in) measurements. Many digital calipers contain

4828-539: The stator is slightly less than 8 times the pitch of each emitter plate, so their intersecting capacitive area is not perfectly aligned but rather forms an interference pattern . As the slider moves, these variable capacitances change in a repeating linear fashion. The slider's circuitry counts these repetitions as it slides and achieves finer resolution using linear interpolation of the capacitances. One model sends 8 periodic pulse-width modulation voltage signals (which appear identical but out of phase by 1 ⁄ 8 of

4899-400: The underlying absolute state of information; the gold standard strives to represent the ground truth as closely as possible. While the gold standard is the best effort to obtain the truth, ground truth is typically collected by direct observations. In machine learning and information retrieval , "ground truth" is the preferred term even when classifications may be imperfect; the gold standard

4970-402: The world's first 8-point tactile electrode system in 1996, a direct segmental analysis method that measures the impedance of five torsos using multiple frequencies. Many BIA products provide partial muscle and fat mass measurements, but not impedance, especially in the torso. Recent advancements such as 8-point electrodes, multi-frequency measurements, and Direct Segmental Analysis, have improved

5041-514: Was used for minute measurements during the Chinese Xin dynasty . The caliper had an inscription stating that it was "made on the gui-you day, the first day of the first month of the first year of Shijianguo . " The calipers included a "slot and pin" and "graduated in inches and tenths of an inch." The modern vernier caliper was invented by Pierre Vernier , as an improvement of the nonius of Pedro Nunes . Inside calipers are used to measure

#852147