Caliper (source code)
= Caliper
A \b[caliper] measures a dimension by relating the separation of contacting measuring faces to a scale or readout. A sliding-jaw caliper has a fixed jaw and a movable jaw; appropriate faces can measure outside dimensions, inside dimensions or steps, while a depth bar can supply a separate depth measurement. These modes use different contact geometries even when they share one slider.<Quick Guide to Precision Measuring Instruments: Calipers by Mitutoyo>[printed p. 16, nomenclature and special-purpose applications]{ref}
A <Vernier scale>, dial or electronic readout converts slider position into a <measurement indication>. It does not remove the need to align the contacts with the desired <length>. For an outside measurement, the opposed faces must meet the intended surfaces without dirt, excessive force or tilt. An inside measurement uses its designated faces and can require geometry-specific corrections; it is not merely the outside-jaw reading with a different label.
An original small-angle calculation shows why jaw geometry matters. Suppose the displacement reference and contact point are separated by $h=40\,\mathrm{mm}$, and a moving-jaw tilt produces angle $\theta=0.002\,\mathrm{rad}$. The resulting offset contribution has magnitude approximately
$$
|e|=h|\tan\theta|\simeq h|\theta|=0.080\,\mathrm{mm}.
$$
It exceeds a $0.05\,\mathrm{mm}$ reading increment. These are stipulated dimensions and tilt, not a measured error for a particular caliper. The primary guide gives the same lever-arm mechanism for <caliper jaw tilt error> and identifies contact force, wear and thermal differences as physical error sources.<Quick Guide to Precision Measuring Instruments: Calipers by Mitutoyo>[printed p. 17, Sources of Error and Moving Jaw Tilt Error]{ref}
A useful check closes clean outside faces under consistent light force, then compares readings at several separations with suitable calibrated artefacts such as <gauge blocks>. Repeating the comparison near different contact positions can reveal a geometry-dependent error that a single zero check misses. Apply a <Vernier zero correction> when using that readout, while retaining uncertainty from the reference, alignment and repeatability.
The <measurement result> concerns the specified object dimension under stated conditions, not just slider displacement. <Thermal expansion> of either the object or instrument, deformation under contact force and the selected faces belong in the <measurement model>. More displayed digits or a finer scale cannot by themselves establish better <measurement accuracy>.
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