Safe-T 45779 Blackboard Protractor

This oversized white plastic semicircular protractor may be used at a chalkboard or whiteboard. A smaller semicircle is cut out of the protractor's interior. Three curved grooves form a third semicircle between these two semicircles. The protractor is divided by single degrees and in three rows of divisions. It is marked by tens from 0° to 180° (left to right) and from 180° to 0° (right to left).
An oversized ruler, or scale of equal parts, divided to mm and marked by single cm from 1 to 10, is on the diameter of the innermost semicircle. A notch for the origin point of the protractor is at the center of this edge. Another scale of equal parts, divided by 16ths of an inch and marked by ones from 1 to 6, is along the outer lower edge.
The protractor is marked: Angles Opening Left (>) Use Upper Scale; Angles Opening Right (<) Use Lower Scale (/) SAFE-T PROTRACTOR® #45779. A recycling logo for plastic type 6 appears in the lower right corner. The protractor retailed for approximately $13 in 2011.
See also ID numbers 1998.0033.02 and 1999.0117.02.
Currently not on view
date made
ca 2000
Associated Date
Safe-T Products, Inc.
place made
United States: Illinois, La Grange
Associated Place
United States: Illinois, Bensenville
Physical Description
plastic (overall material)
overall: 1.5 cm x 47.5 cm x 30.6 cm; 19/32 in x 18 11/16 in x 12 1/16 in
ID Number
accession number
catalog number
Credit Line
Gift of Extra Measures, Inc.
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Data Source
National Museum of American History


Add a comment about this object