Curta II
"The Model I had an 8 column "keyboard" (8 slides), 11 digit results and a 6 digit revolution counter. It was 2.1" in diameter by 3.4" long and weighed 8 oz. The Model II had an 11 column keyboard, 15 digit results and an 8 digit revolution counter. It was 2.6" in diameter by 3.6" long and weighed 12.5 oz. Curtas survived the early electronic desktop calculators due to their portability and lower price, but pocket electronic calculators killed the Curtas in 1972."

David Hicks.

Source: Museum of HP Calculators.

X-Number World of Calculators