The simplest slide rule is just a number line with a movable pointer.
To add 2 numbers, *x* and *y*, simply place the marker on *x* and move it *y* places to the right.

To subtract *y* from *x*, place the marker on *x* and move the marker *y* places to the left.

Slide rules become much more useful when paired with *logarithms*. As you should know, to multiply powers with the same base,
all you have to do is add the exponents. For example, to multiply 2^{3} and 2^{4}, all you need to do is
add the exponents, 3 and 4, to get 2^{7} (which is 128). Conversely, to divide powers with the same base,
simply subtract the divisor's exponent from the dividend's.

In the slide rule below, the powers of 2 are marked above and the corresponding logarithms (base 2) of those values are below.

Now, if you want to multiply 2 powers, say 16 and 32, then you just have to add their logarithms, 4 and 5. So all you have to do is move the cursor to 4 and then move it 5 places to the right. The cursor will land on 9 and its corresponding power, 512, which is the product of 16 and 32.