For example, two position flags should be placed at the same height. For this, a point must be catchable at a different height.
This works by redefining the origin of the AccuDraw. To do this, grab the first flag and drag it to a point at the desired height. Then press an O (for Origin) on the keyboard. Now, the AccuDraw is placed again on this point and the flag can be placed on the new X axis.