Measurement of a length

• Measurement of lengths
• Error on length measurements

A caliper is a device used to measure the distance between two symmetrically opposing sides. A caliper can be as simple as a compass with inward or outward-facing points. The tips of the caliper are adjusted to fit across the points to be measured, the caliper is then removed and the distance read by measuring between the tips with a measuring tool, such as a ruler. The earliest caliper has been found in the Greek Giglio wreck near the Italian coast. The ship 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. By the Han Dynasty (202 BC – 220 AD), the Chinese also used the sliding caliper, which they made of bronze and manufactured each tool with an inscription of the day, month, and year it was made.

Vernier calipers used nowadays provide a precision to a hundredth of a millimeter (or one thousandth of an inch).

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: gives measurements of up to one decimal place (in cm).

Vernier gives measurements up to two decimal places (in cm).

Retainer: used to block movable part to allow the easy transfer of a measurement.

The Vernier caliper allows you to measure external thicknesses, internal diameters and depths of holes to a maximum of 130 mm with a 0.05 mm approximation.

The caliper is made up of a fixed part with scale in mm and a sliding part, with a scale divided into 20 parts (Vernier). The sliding part can move with respect to the fixed part by pushing the blocking lever.

It is always suggested to repeat each measurement several times and then to compute the arithmetic mean of the values.

This is because the sample may only appear to be regular or may be partially deformed by the pressure applied to it. It would be misleading to ascribe to the value of one measurement an accuracy equal to the caliper sensitivity (0.05 mm). Another possible estimation of the error can be obtained by taking the difference between the minimum and the maximum measured values. The vernier scale is constructed so that it is spaced at a constant fraction of the fixed main scale. If you put the two scales together with zero points aligned then the first mark on the vernier scale will be one tenth short of the first main scale mark, the second two tenths short and so on up to the ninth mark which would be misaligned nine tenths.

• Vernier caliper, scale 0 – 160 mm, accuracy 0.05 mm (plastic) — 2213.10
• Specific heat cylinders — 4230.96

• What can you say about these results? Are the values you obtained equal? Why?