Methods to find the center of common shapes and distances.
SLANTING THE RULER METHOD
To divide an odd measurment such as 9 7/16" in half, slant the ruler down until it reads on the 10" mark, 5" will then be the center point, this is similar to dividing a line into equal parts above.
DIVIDING CIRCUMFERENCE A DISK INTO EQUAL PARTS
To divide the circumference of a disk into equal parts wrap a length of drywall tape around it, mark where the ends meet, it is easier on a large disk if the starting end is fastened with masking tape.
Lay the strip out, measure the length, divide into desired parts, marking on inside of paper. Wrap around disk again and transfer the marks to disk.