When measuring the diameter of a hole with a conventional caliper, a geometric error occurs due to the circular shape of the surface. The caliper tips touch the hole at a point above the true diameter, resulting in a reading smaller than the actual value. This difference is called the sagitta, and its calculation allows the measured value to be corrected, obtaining the exact hole diameter.
The same correction is necessary when measuring the center-to-center distance between holes with a caliper. Since the measuring tips do not touch the exact centers, the sagitta error must be added or subtracted depending on the geometry of the part. Considering the sagitta is essential to ensure dimensional accuracy, avoid interferences, and guarantee the proper fit of mechanical components.