Here's a unique vintage adding machine/calculator Designed by Mario Bellini.

By the time electronic calculators began to appear in the mid 1960s, Olivetti had established itself as a manufacturer of innovative, stylish office machines, pioneering several designs of typewriters and electro-mechanical calculators. During this period, Olivetti's reliance on creative designers such as Marcello Nizzoli (designer of the classic Divisumma 24 mechanical calculator) and Ettore Sottsass (designer of the revolutionary Valentine typewriter) produced machines that stood out from the competition. An enduring characteristic of Olivetti machines that began during this period was the use of color and grouping of the various elements to achieve functional simplicity and aesthetic appeal.

In 1974, Bellini broke away completely from the Pop aesthetic and produced severely angled products, which led to the Logos 41,42, and 80 calculators. The calculator was now housed in a charcoal gray box that was split into two planes separating input and output. The unit could be purchased with or without a built-in electronic display (green fluorescent); those with the display had "PD" appended to their model numbers. They may have been Olivetti's first units with a display. In many ways, these models anticipated the "high tech" style that would dominate the design of consumer electronic products from the late 70s until fairly recently.

This unit is in good working order, I've enjoyed using it for the last few years. Could use a new ribbon, available from numerous online sources.