Gauge with 4 arms

Gauge will measure diameter and circumference in mm and inches.
Hollow cavity to store work tools like files, tweezers, gauges, etc.

Holes are used to measure stones and extensions are used to measure mountings.
Gauge has mm and carat measurements.

Reverse side is metric carat measurement.

Capacity:
Diamond - 0.02 to 6 carats
Pearl - ½ to 40 grains