Measure and Scale

From Sigma Design Wiki

Setting the Scale

You can set, or change the scale of a CAD drawing or image by measuring a line in the document or image and entering a known value for its length.

Check Enter Length on the Measure Distance Properties dialog, and the draw a line to measure a distance..

After you enter the distance to measure, the Enter Length of Segment dialog will appear showing the length it measured. Change it the the actual length and the drawing will be re-scaled to reflect the length entered.