The rule is marked with many different measurement markings including the brass slide rule being marked with measurements.
If looking at the rule with the brass slide rule at the top, the lower edge of the bottom arm is bevelled.
This same arm also is marked with a logo, at first glance it looks like the Moore and Wright logo however I don't believe it is as the logo letters are mirrored in reverse to that of the Moore and Wright logo.
These appear to be WM ontop of a D or it could possibly be representing WW ontop of a D.
Condition: all parts move freely including the brass slide rule, some very common warping for a rule of this age, one of the brass keeps has gone, small shrinkage split, please see photos for condition.