By Marion Boddy-Evans
Proportional wheels are used for calculating copy reductions and enlargements.
1. You set the longest dimension of the original on the inner wheel. The scale varies so take your time to get the correct setting if you do not have an even number to start with.
2. Move the outer wheel around to the desired longest dimension. This scale also varies from point to point.
3. Read the percentage reduction or expansion in the window. For a computer, use this percentage to resize your image using percentage settings in your graphics program. To run a copy at the correct size, set the copier to this percentage reduction or enlargement.
For example, your original is 12″x16″ and you want a 4 1/2″ x 5 3/4″ card.
1. Set 16″ on the inner scale (original).
2. Set 5 3/4 on the outer scale.
3. Read 36% from the window.
4. Your final picture will be 5.75″ x 4.3″ because the width scales a bit shorter than you want.
You can adjust the width to 4 1/2″ (12″ original to 4 1/2″ final is 37.5%)but you will lose a bit of the length on the final card. (37.5 percent of 16 is 6″ so you lose 1/2″/37.5 percent or 1 1/3″ from the long dimesion of the original. Decide which side you want it to come from before you proceed.)
Tip from: 94Magna.