Pocket comparator

A pocket comparator is an optical device for measuring and inspection comprising a loupe and a reticle.^[1] The instrument was developed and manufactured by the Bell & Howell Company, but similar instruments of other names are made by other manufacturers.^[2][3]

Reticle of Bell & Howell Pocket Comparator

Typographer Henri Friedlaender at work. Note Pocket Comparator at 01:10.

Bell & Howell Pocket Comparator

It is used for:

• Linear measurements in fractions of an inch^[4][5][6]
• Circular measurements in fractions of an inch
• Radius measurements
• Angle measurements
• Narrow line width measurements^[7]
• Circular measurements in decimals of an inch
• Linear measurements in inches
• Linear measurements in millimeters

Measurements are performed by bringing the surface of the reticle as close as possible to the work inspected.^[8]