Vernier calipers are not alone.

Vernier calipers are not alone because they don't read. Vernier calipers do not estimate readings, that is to say, when the caliper positions are not corresponding, it is necessary to estimate readings in the middle position. There are such stalks in physics.

Vernier caliper is a measuring tool for measuring length, inside and outside diameter and depth. The vernier caliper consists of a main ruler and a sliding vernier attached to the main ruler. The main ruler is usually in millimeters, while the cursor has 10, 20 or 50 scales.

According to different divisions, vernier calipers can be divided into ten-degree vernier calipers, twenty-degree vernier calipers and fifty-degree vernier calipers. The cursor of 10 is 9mm, that of 20 is 19mm, and that of 50 is 49mm. There are two pairs of movable measuring claws on the caliper and the main ruler of the vernier, namely, the inner measuring claw and the outer measuring claw. The inner measuring claw is usually used to measure the inner diameter, and the outer measuring claw is usually used to measure the length and outer diameter.

Among all kinds of measuring instruments, vernier caliper, as a widely used high-precision measuring tool, is the extension and expansion of the ruler originated from China. In ancient times, wooden poles or ropes were used to measure the length, or the methods of "stepping" and "spreading hands" were used. After the establishment of the system of length units, the marking ruler appeared.

This ruled ruler was used in ancient Egypt in 3000 BC and Xia and Shang Dynasties in China in 2000 BC. At that time, it was mainly made of ivory and jade. It was not until the appearance of bronze ruler that this "advanced" measuring tool was widely used in production and astronomical measurement.