Tacro Proportional Dividers

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The pointers on this German silver drawing instrument are held in place with screws, meaning that they can be adjusted and replaced. The points are 1-1/8" and 1/2" long. The front slide has scales for lines, running by ones from 1 to 10, and for circles, irregularly numbered from 6 to 36. Thumbscrews on both sides adjust the instrument along a gear and tooth mechanism (or "rack movement") on the back slide. The front slide is marked: TACRO INC. (/) GERMANY. The case is covered with black leather and lined with blue velvet. It is unlocked by pulling out a button on the right side of the case. The case is marked on the top: TACRO. It is also marked: 4130. The case is marked on the bottom: Made in Germany.
Tacro is a manufacturer of drawing instruments apparently established in the 20th century. According to online auction records, it marked its products as made in West Germany from about 1950 to 1991. Thus, this object probably dates to the 1930s or 1940s. As of 2012, Tacro continues to make these proportional dividers.
Currently not on view
date made
ca 1940
place made
Physical Description
aluminum (overall material)
felt (overall material)
wood (overall material)
steel (overall material)
overall: 2 cm x 22.8 cm x 3.8 cm; 25/32 in x 8 31/32 in x 1 1/2 in
ID Number
accession number
catalog number
Credit Line
Gift of Ursula N. Forbes
Drawing Instruments
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Dividers and Compasses
Data Source
National Museum of American History


How does this work with the circle markings. The proportional divder

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