||This is one of the series of
inexpensive school slide rules (Schul-Rechenstab) that Faber-Castall
made. They do not have the manufacturing date imprinted on the
back. I am not able to date this rule yet. Looking at the box I would
estimate the 1910-1935 period. To be confirmed!
The celluloid of this slide rule looks very cheap:
more like a thick layer of white paint.