Midpoint

1. Start with two points, $$P_1$$ and $$P_2$$.

2. Draw a line segment $$\overline{P_1 P_2}$$

3. Draw circles $$\overset{\frown}{P_1 P_2}$$ and $$\overset{\frown}{P_2 P_1}$$. Note the intersections of the circles.

4. Draw a line segment connecting the intersections of the circles. Where it intersects line segment $$\overline{P_1 P_2}$$ is the midpoint.

AlDraw also has a shortcut for finding midpoints. It is under the "Shortcuts" menu, and its hotkey is alt-1.