The Bowmar Math Mate II is a handheld calculator from 1975. It measures approximately 71mm x 135mm x 25mm and weighs about 100g without the battery. The Math Mate II is powered by a single 9V battery or can use an AC adapter.
The calculator’s case is made of white plastic with rounded edges and corners. It has a large red plastic display filter that makes the 8-digit LED display very bright and easy to read. The keyboard surround is brown plastic with raised silver lettering. The keys have a short travel distance and make a prominent click when pressed.
The Math Mate II performs the four basic arithmetic functions – addition, subtraction, multiplication, and division. It can handle percentages and has a four function memory. The memory allows you to store a number and recall it later for use in calculations. There are keys dedicated to memory operations like store, recall, and exchange with the display.
The display shows up to 8 digits plus an additional LED for negative numbers and overflow indication. Input overflow is suppressed – entering more than 8 digits is ignored. Negative numbers are displayed with a minus sign that travels into the leftmost ninth digit position. This allows full 8 digit negative numbers to be shown.
The calculator employs some shortcuts that were common at the time. There is automatic constant on all four arithmetic functions, meaning you don’t need to re-enter a constant each time. It suffers from the pseudo fixed decimal bug – if you enter a decimal number with zeros after the decimal point, it will show as fixed decimal places until you perform further operations. There is also a divide by zero error that shows zero and an error code, but it can be recovered by pressing the clear key.
Overall the Math Mate II is a competently designed calculator for its time. The case design allows comfortable handheld or desk use. The display is brighter and wider viewing angle than typical bubble LED types. The logic and key operations are reasonable despite the quirks it shares with other basic calculators of the mid 1970s.