This technical bulletin from Mitutoyo America Corporation focuses on the accuracy and calibration of digital, dial, and vernier calipers. The bulletin is based on the American national standard (ANSI) ASME B89.1.14-2018, which covers the most important metrological characteristics of calipers. These characteristics are called the partial surface contact error (E) and the scale shift error (S). The partial surface contact error applies to measurements made using the outside measuring faces, while the scale shift error applies to measurements using any other measuring faces available on the caliper.
The ASME B89.1.14 standard provides default specifications for the E and S errors, which are the maximum permissible errors (MPE) for the E and S errors. Mitutoyo specifications for calipers are similar to these values, and many customers may find the best practice to adopt these values for their own caliper calibrations.
The specifications are a function of the measured length, L, not the overall measuring range of the caliper. The decision rule for these specifications is Simple Acceptance with a test uncertainty ratio (TUR ? 4) and apply at 20°C. For more information on educational opportunities, visit
Calibration and verification of calipers are crucial to ensure they conform to accuracy specifications. Conformance verification tests for EMPE and SMPE are outlined in ASME B89.1.14. EMPE requires three to five test points, depending on the caliper's range, covering at least 90% of the measurement range. SMPE requires verification for all modes of operation with at least a single test point. The reference standard for inside measurements is typically a caliper checker, ring gage, or gage blocks and accessories. Cross-knife-edge measuring faces can cause errors when measuring small internal diameters. ASME B89.1.14 requires an additional test using a 0.2 in diameter ring gage for all calipers with measuring ranges up to 12 in (300 mm). Test points should be carefully selected and cyclic errors may occur in used calipers. Mitutoyo Calibration Laboratory in Aurora, Illinois offers accredited calibrations and measurement standards.