Pocket rule for arithmetical and measurement conversion - is in form of wallet which opens into two parts for tabular display of multiples and equivalents

摘要

The rule has a flat pocket or case on a wall of which are formed aligned windows or transparent zones. The windows or zones are uniformly spaced on the case. Slides are fitted longitudinally into the case. The slides have inscribed on them numerical or graphical indications relative to a multiplication table or an equivalence scale. These indications are aligned and uniformly spaced in a similar fashion to the windows. The case has two parts one for multiplication the other for equivalents. The two parts can be folded over onto each other like a wallet.