Did you get the answer 8.5?  If you did, that's fantastic!  If not, you need to take things a bit s..l..o..w..e..r.  If you're really not sure read the explanation below.

Let's go through our steps again ...

1. We line up the left index (C1) with the first number 3.4 (on the D scale).
2. Slide the cursor to the second number, 2.5 on the C scale.
3. Now read the answer below the 2.5 and you find 8.5 (on the D scale).

Are you ready?  If you are click here to go back to the lesson.