Specialized calipers, such as those from Presidium Instruments or other analog and digital brands, are indispensable tools for gemologists and jewelers. They are used to measure with millimeter precision, estimate carat weight, verify cut proportions, and check ring sizes.
The distinguishing features of these specialized measuring instruments include:
Measuring range and precision
Unlike regular calipers, these have a very high resolution, typically down to (0.01text{ mm}) for digital variants and (0.1text{ mm}) for analog ones. They are generally capable of measuring up to 20–25 millimeters.
Direct conversion to carats
Many gauges – most notably the classic Presidium Dial Gauge – have a built-in scale that directly converts the size in millimeters to the estimated carat weight (carat) for round brilliant-cut diamonds. It also includes tables for other cut shapes (such as oval, teardrop and emerald) to calculate the weight without having to remove the stone from its setting.
Specially adapted measuring tips
To avoid damaging the stones, the ends of the caliper (anvil or probe) are usually designed with very thin, beveled tips. This makes it possible to reach between claws and metal settings. Many models also come with a special attachment for measuring high-positioned or hard-to-reach stones.
Mechanical durability
Since the tools are used frequently and require absolute precision, the mechanisms are protected. For example, Presidium manufactures instruments with patented, lubrication-free racks and hardened metal parts that prevent wear over time.
