Marking a Scale Factor Using Three Colinear Points

Marking a Ratio Using Three Collinear Points

1. Select three collinear points in your sketch. The points must be in a straight line.

2. Choose Mark Ratio from the Transform menu.

You will see a brief animation confirming that the ratio has been marked.

When you mark three collinear points, A, B, and C, as a ratio, Sketchpad dilates by the ratio of signed distances AC/AB. If B is on the same side of A as C, the signed ratio of distances is positive; if B is on the opposite side of A as C, the ratio is negative. You may wish to use the Ratio command in the Measure menu to display this ratio numerically. One handy way to remember the role of the three selected points is to think of them as determining a ratio that, if the first selected point was the marked center, would dilate the second selected point to the location of the third selected point.