The Atlas R100 is a handheld calculator from the late 1970s. Manufactured by the German company MBO, it has a sleek, wedge-shaped case made of dark brown plastic. The front is dominated by a metal surround wrapping around the edges, with an oversized green plastic display filter slightly protruding over the top.
This calculator measures approximately 80mm x 134mm x 19mm and weighs 132g without batteries. Power comes from two AA batteries or optionally from a 3V DC adapter. The display utilizes an 8-digit green vacuum fluorescent tube, with a ninth digit for indicating negatives, errors, and memory status.
Feature-wise, the Atlas R100 is a basic 4-function calculator with percentage keys, a square root function, pi constant, sign change, and a single memory register for storage. Despite its simplicity, the R100 feels solid with its metal trim and loud, clicky keys. The glossy brown keyboard surround has printed orange and silver labels for the functions.
Internally, the R100 uses a NEC D1803C processor chip from 1977 along with NEC display and other discrete components. The keyboard sits loosely on the main circuit board and connects through several wiring posts. There is no logic to recover from errors like overflow or division by zero. The change sign key can be used mid-number entry but not before entering a number. Overall, the R100 demonstrates no particular bugs or quirks in its operation.
While limited in features compared to more advanced calculators of the era, the Atlas R100 delivers on its promise as a rugged, well-built basic calculator. Its high-quality construction and unique design have stood the test of time over 40+ years since its release. For the student or professional needing portable calculating power, the R100 provided solid if unexceptional performance.