Parisian Novelty

Profit Calculator

Log scales for salesmen. The yellow scale is a straightforward D scale. The outer one is an incomplete C, but the labels are 100*(C-1) to turn them into percent increases (e.g. 1.5 becomes 50%) . And the inner scale is similarly and incomplete CI.

In tiny print under the "Profit on Selling Price" instructions is "Copyright 1960 Parisian Novelty Co, Chicago". The company, established in 1898 and only shuttered in 2008, is best known for making plastic-laminated buttons & badges, but it turns out they also custom-manufactured slide rules! Here's a medical rule, and on page 2 of this PDF is a picture of a concrete calculator.

The construction reveals that this wasn't specifically made for the Friedrich Air Conditioning company. There are 3 layers: the top is clear plastic on which have been printed just the outer- and innermost scales (tan), leaving a clear band between them and a clear circle within the inner scale. The bottom layer is card stock on which has been printed the middle scale (yellowish). Sandwiched between these two scale-bearing layers them is a small disk on which is printed "Friedrich Air Conditioning". Plainly, to customize the calculator for any company, Parisian just had to print different little disks to fasten between the scale-bearing disks.