A rare full brass folding rule of 22 French inches, datable from early 18th century.

If we find usual later example in ivory or boxwood the early example if full brass seems quite rare in private hands and in public institutions.

The present example is French divided with three scales on two sides :

-1 to 22 French inches on one side

-And in the same side but up side down : divided in quarter : “quart”, “demy quart” and “seize” & divided in third : “tiers”, demi tiers” and “douze”.

The folding rule is classicaly built with four pieces (here of brass) hinged with three joints.

It measures folded 15,7cm lenght and 59,5cm.

For an illustration of this kind of folding rule in 1701, see the last picture extracted from Tuttel, Mathematical made easie.