Brunsviga
"Midget" Calculator
Add,
subtract, multiply, divide and square root. Allows 9 digit by 10
digit calculations. Patented
in 1906. 
Thacher's
Calculating Instrument Equivalent
of a 360" long slide rule, allows calculations to a precision of
1:10,000. Patented
in 1881. 
Fowler's
"Magnum" Calculator
A
multiscale circular slide rule. Early
to mid 1900's.

The Fuller
Calculator
Equivalent
of a 500" long slide rule. Allows calculations to a precision of 1:10,000.
Early
to mid 1900's. 
Otis
King's Patent Calculator
Equivalent of a 60" long slide rule

Curta
Calculator
Add,
subtract, multiply, divide and square root. Allows 6 digit by 8
digit calculations. The "field crew" calculator of the
1950's and
60's.

Traditional
6" and 12" Slide Rules
