Vintage EFZET pocket mechanical calculator, a compact German “slide adder” used for performing arithmetic calculations before electronic calculators existed.

This device is a private-label version of the PRODUX ST calculator, produced in Germany in the early 20th century and sold under the EFZET brand. These ingenious mechanical calculators allowed users to perform addition and subtraction by sliding numbered metal rods using a small stylus.

Housed in its original folding pocket case, the calculator was designed to be carried by accountants, engineers, merchants, and office workers for quick calculations.

Features

• Brand: EFZET

• Type: Pocket mechanical slide calculator / slide adder

• Model: Produx ST variant

• Country of Manufacture: Germany

• Era: circa 1920s–1930s

• Metal calculator plate with numbered slide rods

• Folding pocket case

• Original stylus included

How It Works

Numbers are entered by sliding the metal rods with the stylus. The calculator automatically handles carrying digits during addition and subtraction using a clever mechanical design.

Condition

Vintage antique condition.

• Shows wear consistent with age and use

• Case has visible wear and edge damage (see photos)

• Calculator face shows age and patina

• Stylus included

Please review all photos carefully as they form part of the description.

Size

Approximately pocket-sized (see ruler photo for measurements).

Historical Note

Mechanical slide calculators like this were widely used in business and engineering offices throughout the early 20th century. The EFZET version is a collectible variation of the well-known Produx and Addiator slide calculators.