Divide a square in 4.
Draw a square ABCD using the same method shown in "Draw a square."
Draw circles with your compasses centring at D, A and C. Eyeball the width to be more than half the length of an edge.
The circles intersect (cross each other) at M and N, O and P.
The circles intersect (cross each other) at M and N, O and P.
Draw lines with your straightedge through M and N right across the square. Do the same through O and P. These lines divide the square in 4, and divide each edge of the square in 2, and find the centre of the square.
Geometry: using only compasses and straightedge