Olivetti Divisumma 28 (1973)
The sister of the Olivetti 18
This is the Olivetti Divisumma 28, an Olivetti calculator from 1973. Like the Divisumma 18, it is covered with a soft rubber membrane.
It has no display; results are printed on this metallic paper.
Like the Divisumma 18, this one was also designed by Mario Bellini, and as was customary for Olivetti at the time, he collaborated with a team of people: Dario De Diana, Alessandro De Gregori, Derk Jan De Vries, Antonio Macchi Cassia, Gianni Pasini, and Sandro Pasqui.
It wasn't aimed at a wide market and was quite expensive, but it was quite successful. It's on display at the Museum of Modern Art in New York, along with its sister model, the Divisumma 18. It has small, round, rubber-coated keys that are pleasant to the touch. It can perform the four basic mathematical operations (addition, subtraction, multiplication, and division), with a capacity of twelve digits.
Use special metallic paper, not regular calculator paper.
If you'd like to see some details and how it works, here's a video.
