I have a circular slide rule, but I can't figure out what the markings on the back are used for.
The front face has two logarithmic scales, the outer one runs from $1$ to $100$ (exclusive), and the inner scale runs from $1$ to $10$, so it's easy to take square roots or square numbers using the front face.
Here's a demonstration of multiplying $4$ by $2$ . The slide rule doesn't have instructions, so I'm just guessing on what the proper procedure is for multiplying.
First, rotate the multiplicand so it's right under the marker under the top button, and rotate the needle so it points to $1$, the initial multiplier.
Next, rotate so that the needle points to the desired multiplier (in this case $2$). The top marker now points to $8$ as desired.
So, that all makes sense, but the back of the slide rule is completely inscrutable to me.
It seems to have multiple scales, with the innermost scale arranged in some kind of spiral. The scales appear to logarithmically spaced, similar to the scales on the front. However, I can't figure out what computation the scale on the back is supposed to be used for.