It is easy to eyeball divisions of 2 and 3 by hand, and get results with high degrees of accuracy. A division of 4 can be accomplished by dividing by 2 twice.

It is easy to eyeball divisions of 2 and 3 by hand, and get results with high degrees of accuracy. A division of 4 can be accomplished by dividing by 2 twice. It is not easy to eyeball divisions of 5 by hand; you pretty much need to use a ruler for that to get results of tolerable accuracy.