Instructions for Constructing $90\text{°}$ Angles

1.

Draw a straight line $l$ and make a point $P$ on the line.

2.

Put the point of the draft compass on $P$ and make an arc that intersects the line $l$ on both sides of $P$.

3.

Call the intersections $A$ and $B$.

4.

Put the point of the draft compass on $A$ and make a small arc above $P$.

5.

Without changing the distance between the legs of the draft compass, do the same thing on $B$. Make sure the two arcs intersect.

6.

Draw a line from the point $P$ through the point where the two small arcs intersect. This is a $90$° angle.