N4081 Either Index May Be Used

6. Either index may be used. It may happen that a product cannot be read when the left index of the C scale is used in the rule of §5. This will be due to the fact that the second number of the product is on the part of the slide projecting beyond the body. In this case reset the slide using the right index of the C scale in place of the left, or use the following rule:

Rule. When a number is to be read on the D scale opposite a number of the C scale and cannot be read, push the hairline to the index of the C scale inside the body and draw the other index of the C scale under the hairline. Then make the desired reading.

This rule, slightly modified to apply to the scales being used, is generally applicable when an operation calls for setting the hairline to a position on the part of the slide extending beyond the body.

If, to find the product of 2 and 6, we set the left index of the C scale opposite 2 on the D scale, we cannot read the answer on the D scale opposite 6 on the C scale. Hence, we set the right index of C opposite 2 on D; opposite 6 on C read the answer, 12, on D.

Again, to find 0.0314 × 564,
                              to 314 on D set the right index of C,
                              push hairline to 564 on C,
                              at the hairline read 1771 on D.

A rough approximation is obtained by finding 0.03 × 600 = 18. Hence the product is 17.71.

EXERCISES Perform the indicated multiplications.

3 × 5.
2. 15.77

3.05 × 5.17.
3. 3525

5.56 × 634.
4. 42.1