Safe-T 45762 Blackboard Compass


This is an oversized form of the Safe-T Compass (1998.0033.03), for use at a blackboard or dry erase board. It is a white plastic wedge-shaped instrument, with a rotating clear plastic disc set inside the wide end of the wedge. Both long edges of the wedge have a row of 9 circular holes. The holes are marked for the radius of various circles, from 1" to 5". To draw a large circle, a marker or piece of chalk is placed in the desired hole and the instrument is rotated while the user holds the disc. Note that the circle radii are those that may be drawn with the pocket-sized version of the instrument. This compass actually draws circles with radii from 3" to 15". One long edge of the wedge has a scale marked for four inches, divided to 16ths of an inch. The other edge has a scale marked for ten centimeters, divided to millimeters. Both scales are oversized.

Seven holes are in the disc. A piece of black rubber in the center hole attaches the instrument more securely to the blackboard. To draw a small circle of up to 3/8" radius, a marker or piece of chalk is placed in the desired hole and used to rotate the disc, while the wedge is held in place. Again, this instrument actually draws larger circles. The wedge is marked: SAFE-T (/) COMPASS® (/) Bensenville, IL 60106-0316 (/) #45762 Pat. #5,615,485. It is also marked: π = 3.1416 (/) A = πr2 (/) C = πd. The donor applied for the patent listed on this instrument in 1995 and simultaneously assigned it to Safe-T Products, Inc. A company catalog in the accession file indicates the compass sold for $18.95 around 2000.

According to the donor, the Safe-T compass, invented by Jack Kettlestrings of Naperville, Ill., was the first product of Safe-T Products, Inc., and Extra Measures, Inc. These related companies were established in the northwest Chicago suburbs in 1992 and 1997, respectively, to sell drawing instruments that were safe for children. For instance, as the donor noted, the compass is too wide to be swallowed, and the plastic bends, but does not break. This concern for safety is reflected in numerous products of the time. In 2006 and 2007, Safe-T was absorbed into Classroom Products Warehouse, and Extra Measures was taken over by Learning Resources, Inc. These firms were next-door neighbors in Vernon Hills, Ill., as of 2012.

References: Accession file; Bruce Stoneberg, "Instruments for Drawing Circles" (U.S. Patent 5,615,485 issued April 1, 1997); "Corporate and Limited Liability Company Name Search," Office of the Secretary of State for the State of Illinois,

Date Made: before 2000

Maker: Safe-T Products, Inc.

Location: Currently not on view

Place Made: ChinaSold: United States: Illinois, Bensenville

Subject: MathematicsDrawing InstrumentsEducation


See more items in: Medicine and Science: Mathematics, Science & Mathematics, Dividers and Compasses


Exhibition Location:

Credit Line: Gift of Extra Measures, Inc.

Data Source: National Museum of American History

Id Number: 2000.0160.04Accession Number: 2000.0160Catalog Number: 2000.0160.04

Object Name: compasscompass, drawing

Physical Description: plastic (overall material)Measurements: overall: 1.6 cm x 48 cm x 16 cm; 5/8 in x 18 29/32 in x 6 5/16 in


Record Id: nmah_904392

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