Old Tavernier-Gravet milk dry extract calculation rule, Jean Pien model

Old ruler for calculating the dry extract of Tavernier-Gravet milk, Jean Pien model.

This model used in agriculture makes it possible to instantly obtain the total dry extract and the defatted dry extract of whole or skimmed milk.

This very unusual slide rule model dates from after 1943.

The ruler is in very good condition and its cardboard box is present.

There are some small signs of yellowing on the plastic.

The original instructions are missing.

I provide a photocopy of the instructions for use.

Length: 29.5 cm.

Width: 4.1 cm.

Used item.