Parallel or Rolling Rules were used in draughting to draw parallel lines and in navigation to mark bearings on a map.
The heavy lacquered brass ruler has two wheels connected by a long axle that allow it to be rolled to a new position while its edges remain parallel to their original orientation.
This one is signed by the Sydney instrument distributor and maker E. Esdaile. Unusually, it is marked 'E.ESDAILE MAKER' to emphasise that it was actually made by the firm.
Markings on the case may suggest it was made around 1921.
See also Item 2053.