The Casio 101-MR is an early handheld calculator from 1974. With a wide and bulky design, it measures 116mm x 154mm x 37.5mm and weighs 312g without batteries. The case consists of a rear dark brown plastic section and a front beige glossy plastic cover. There is a black plastic display area tilted slightly upwards, framed by white lines and silver painted letters displaying the Casio name and model number.
The 101-MR is powered by 4 AA batteries or can use an optional AC adapter. It has a 10 digit vacuum fluorescent display, allowing for full 10 digit calculations. The display also has an extra symbol section on the left showing the status of features like negative numbers, memory, and constant.
As an early calculator, the 101-MR has a limited feature set. It can do basic four function math, percentages, square roots, and memory storage. It also has options for decimal point selection, rounding, and using a constant. The keyboard uses a Reverse Polish Notation input style, which was common at the time.
Inside, the 101-MR utilizes a Hitachi HD32612P processor and a separate keyboard circuit board connected by wires. The vintage logic provides some quirks to using the device. Overflow or errors will lock up the calculator, needing a full reset. It also allows negative square roots, causing the display to flicker.
The 101-MR shows the transition period when handheld calculators were still large devices limited by the technology of the era. By 1975, Casio had introduced smaller and more powerful models. But the 101-MR represents an important milestone in bringing complex math calculations into a portable consumer product.