Page "Slide rule" Paragraph 15

Operations may go " off the scale ;" for example, the diagram above shows that the slide rule has not positioned the 7 on the upper scale above any number on the lower scale, so it does not give any answer for 2 × 7.

In such cases, the user may slide the upper scale to the left until its right index aligns with the 2, effectively dividing by 10 ( by subtracting the full length of the C-scale ) and then multiplying by 7, as in the illustration below: