Advice needed in measuring

[ChattanCat]

Here is one that I learned a long time ago. Make a square, or close to it, with a string. Try to make sharp corners. Now make all the sides the same length (each side will be 1/4 the total length of the string. Now measure from the lower left corner to the upper right corner. Also measure the lower right to the upper left corners. Adjust until the corner to corner measurements are the same. Make sure you keep each side length 1/'4 of the total length (this is key).

I learned this when we were installing an overhead conveyor system. Each pillar needed to be accruatly located. We measured, snaped a chalk line, then measured. Worked like a charm.