Caliper

Calipers are among the most common measuring instruments in manufacturing, machining, and quality inspection. Modern digital calipers use a capacitive or inductive linear encoder to provide electronic readings, while dial calipers use a rack-and-pinion mechanism and vernier calipers rely on a graduated vernier scale for interpolation. Most calipers can measure external dimensions (using the main jaws), internal dimensions (using the smaller jaws or knife edges), depth (using the depth rod), and step heights.

Calibration of calipers involves checking their accuracy at multiple points across their range using gage blocks as reference standards. Key calibration points include zero (jaws closed), several intermediate sizes, and near the maximum range. The calibration procedure also checks jaw flatness, jaw parallelism, and the zero-setting function. Common sources of error include jaw wear, debris between the jaws, temperature variations, and excessive measuring force.

For calibration management, calipers typically require calibration intervals of 6 to 12 months depending on usage frequency and the criticality of measurements. Because calipers are handheld instruments used in shop environments, they are subject to damage, contamination, and thermal effects that can degrade their accuracy. Proper use techniques — including clean measurement surfaces, consistent measuring force, and temperature equilibration — are essential for reliable results. Many organizations maintain both shop-grade calipers for general use and inspection-grade calipers for critical measurements.