Let's have a closer look at part of the CI scale ...

 Notice how the numbers get smaller when we read it from left to right, notice also, that it matches up with the C scale underneath it.  This is because it is the inverse of the C scale.

Using this scale we can quickly find reciprocals, for example what would be the reciprocal of 8?

1. We move the cursor to 8 on the CI scale.
2. The we read the reciprocal on the C scale at 0.125.

Well this makes sense ...

We can see that the slide rule has given the answer to the reciprocal in a decimal form (well it can't really show the fractions can it).

This scale can be a little difficult to read when we first start because it's very different to the other scales and sometimes it's a bit hard to work out where the decimal point should be in our answer.  However, with practice, this scale won't cause you any more problem than the other scales on your slide rule.

Let's look at one more example ...

What is the inverse of 1.6?

1. Move the cursor to 1.6 on the CI scale.
2. No read the answer of 0.625 on the C scale.

 Okay, we might leave our CI scale for a while.  It might seem a little complicated at the moment, but it can be used to make things like multiplication and division a little bit quicker.

We'll come back to it when we start looking at some of our problems later.