Supremathic

Made by French company Stephens, there were two types of Supremathic featuring polished aluminum (fingerprint magnet) construction. .

Both types had the same front, featuring two concentric dials used for multiplication and division. The back of both types have 5 windows and vary only in what they're for. On one, they correspond to S, T, ST, A and K scales. On the other are 3 log log scales, plus S and T. This is the latter type.

(After writing the following description, I recorded a video showing how the Suprematic works because it's so worth actually seeing. So read on, or scroll down to find the vid at the bottom of the page.)

The two dials are stacked disks, one a bit larger than the other, that rotate on a common center. The larger, bottom dial can be turned infinitely in either direction by its knurled rim which is exposed from about 11 o'clock to 4 o'clock on the device. As it is turned, a counterclockwise scale (call it D) rotates under a transparent window marked with a fixed red cursor at 12 o'clock.

The smaller, top disk can be turned by the big knob. The disk is entirely clear, except for one red and one black cursor. It turns counterclockwise infinitely, but when turned clockwise it hits a stop when the red cursor is at 12 o'clock As it is rotated, the cursors glide over a fixed pair of scales, numbered in the metal with tick marks on paper glued to the metal. The outer of these two scales (call it CI) runs counterclockwise, and the inner one (C) runs clockwise. (The outer one is not numbered in the arc occupied by the window with the fixed cursor.) Note that the clear disk sits over the inner scale numbers and both sets of tick marks

The trick is, the two dials are linked, probably by friction, such that rotation of the bottom one turns the top one but not vice-versa..

So, to use it, one first turns the bottom disk until either one's multiplicand or dividend is under the fixed cursor. Next, one turns the top disk clockwise until it hits the hard stop and its red cursor is aligned under the fixed cursor. Last, one starts to turn the bottom dial again, counter-clockwise! Doing so carries the top disk's red cursor counter-clockwise along with it, while the numbers on the D scale, under the fixed cursor, descend.

If doing division, one stops when the top dial's red cursor is at the divisor on the CI scale; the numbers under the fixed cursor have descended equally as the cursor on the top disk was moved upward over the CI scale. If one is doing multiplication, one stops when the top disk's red cursor is at the multiplier on the C scale - I think of it as dividing by the inverse. In either case, the answer is located under the fixed cursor - whereupon one can again turn the top dial clockwise until it stops and thus be ready to perform the next calculation. Very clever.

Click on pictures for hi-res images