The Bohn Omnitrex was an early compact calculator released in 1973 by the Bohn Rex Rotary company. It retailed for $100, which was quite expensive at the time. The Omnitrex measures 68mm x 127mm x 17-22mm and weighs 272g without batteries. It is powered by five AA batteries or can use an AC adapter plugged into the side.
The Omnitrex has a two-piece dark gray plastic case with a cream-colored front panel. The front panel houses two switches and the keyboard, which sits flush. The keyboard uses typewriter-style keys with short travel and a positive click. The eight green vacuum fluorescent tube digits are protected by a large green plastic filter angled for optimal visibility.
The Omnitrex performs the basic four functions – addition, subtraction, multiplication and division – along with percentages and sign change. It can switch between floating decimal and fixed decimal modes for financial calculations. The nine-digit display allows eight digits plus a negative sign. Input overflow is suppressed and divide by zero errors are indicated.
Internally, the Omnitrex uses a Rockwell A1032PD microprocessor and nine ISE glass VFD tube displays. The keyboard connects via a flex cable. Construction quality appears good for the time.
The Omnitrex employs an archaic semi-RPN logic that requires entering operands before operators. Its fixed decimal mode also has a bug that improperly formats decimal numbers. However, its bright VFD display and compact wedge-shaped case were advanced features for an early 1970s calculator. The Bohn Omnitrex shows both the rapid pace of innovation and limitations of very early calculator technology.