Pocket comparator

Bell & Howell 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.

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]

References

1. "The Pocket Comparator - A New Optical Measuring Instrument". in: Electrical Engineering (Volume 69, Issue 3, p. 220) March 1950 https://ieeexplore.ieee.org/document/6433729/
2. " by Marcus Bowman Crowood, 31 August 2015, Crafts & Hobbies
3. "Low price measuring magnifier uses real glass reticle", Journal of the Franklin Institute, 1955, Vol. 259(6), pp. 516–516 [peer reviewed journal]
4. Charles C. Ryerson and Anthony J. Gow: Ship Superstructure Icing: Crystalline and Physical Properties in: US Army Corps of Engineers® Engineer Research and Development Center (August 2000) p. 14
5. van Altena, W. F., Low-luminosity members of the Hyades cluster. Astronomical Journal, Vol. 71, p. 482–512 (1966)
6. I. B. A. Menown, G. MacKenzie and A. A. J. Adgey, Optimizing the initial 12-lead electrocardiographic diagnosis of acute myocardial infarction, European Heart Journal (2000) 21, 275–283
7. DEPARTMENT OF THE ARMY EM 1110-2-2002 U.S. Army Corps of Engineers: EVALUATION AND REPAIR OF CONCRETE STRUCTURES p.2-11 https://www.publications.usace.army.mil/Portals/76/Publications/EngineerManuals/EM_1110-2-2002.pdf
8. The Pocket Comparator: A New Measuring Instrument, in: INDUSTRIAL QUALITY CONTROL VOL.6 NO.5, March 1950 pp. 22-23