In 1976, Braun added pocket calculators to its range, just around the time they were becoming popular. As is so often the case at Braun, the company did not invent a completely new product, but initially only slightly modified a model from the Japanese company Omron. Two designers, Dietrich Lubs and Dieter Rams, developed a user interface for the device that was as easy to use and understand as possible. This required simplification and a focus on the most important functions, which was achieved primarily with color-coded buttons. The color scheme is as functional as it is visual: high-gloss black for the main buttons, brown and a muted green for the functions, as well as a brighter green and the complementary color red for the on/off switch and yellow for the sum button–probably the most frequently used button on a pocket calculator. The latter is not only immediately visible and intuitive to use thanks to the color scheme but has also become the unmistakable trademark of a Braun pocket calculator. To make operation more pleasant, the buttons were designed to be convex, i.e., slightly raised. Brief operating instructions can be found on the back of the device.