Trebla (ca 1930)
Albert Steinmann, La Chaux de fonds, Schweiz
dimensions...........17,3 x 10,7 x 1 cm
weight..................290 g
material................brass/ bakelit
digits ...................9
single sided
including a pencil
There is a metal grooved plate that flips from addition to subtraction (see next picture).
When you read Trebla backwards, you see Albert (Steinmann).