The first slide rulers were developed in the C17th, for mathematical calculations. They were used consistently from this date until 1974, when they were replaced by the scientific calculator. The middle section moves between scales on top and bottom of the scales, and then an independent clear plastic slider is moved to allow the calculation to be read.
These 10” slide rulers [250mm] were made for the office; they are larger and allow more complex calculations that the smaller 5” portable scale rules […yes..they will appear in a previous post…I can’t help it…I love them!]
The Hemmi slide [topmost in the image] has a bamboo structure, with a plastic laminate covering; whilst the later slide rules are all solid plastic. All slide rules come in their own boxes [some with original operating instructions] and some have their original owners names incised on the box.
For sale: $AUD85