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The vernier caliper is used to make semi- accurate measurements for inside, outside and depth dimensions. Standard vernier callipers are available in sizes 150mm to 250mm. Custom- made vernier callipers can be made to specifications if required. Graduations, (that determine the accuracy of the instrument) are usually 0,02mm or 0,05mm on the vernier scale. A calliper can be as simple as a compass with inward or outward-facing points. The tips of the calliper are adjusted to fit across the points to be measured, the calliper is then removed and the distance read by measuring between the tips with a measuring tool, such as a ruler. It is used in many fields such as mechanical engineering, metalworking, woodworking, science and medicine. The vernier, dial, and digital callipers give a direct reading of the distance measured to high accuracy. They are functionally identical, with different ways of reading the result. These callipers 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 the reading. This would be a simple calibrated calliper; but the addition of a vernier scale allows more accurate interpolation, and is the universal practice; this is the vernier calliper. Vernier, dial, and digital callipers 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 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 callipers commonly used in industry provide a precision to 0.01 mm ( micrometres), or one thousandth of an inch. They are available in sizes that can measure up to 1,829 mm (72 in).
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Parts of a vernier caliper:
- Outside jaws: used to measure external diameter or width of an object
- Inside jaws: used to measure internal diameter of an object
- Depth probe: used to measure depths of an object or a hole
- Main scale: scale marked every mm
- Main scale: scale marked in inches and fractions
- Vernier scale gives interpolated measurements to 0.1 mm or better
- Vernier scale gives interpolated measurements in fractions of an inch
- Retainer: used to block movable part to allow the easy transferring of a measurement
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