It's analogous to measuring the length of something by using the length of your forearm Yes, it's less precise than using a tape measure, and it often gives an

It's analogous to measuring the length of something by using the length of your forearm Yes, it's less precise than using a tape measure, and it often gives an inaccurate answer (sometimes extremely inaccurate) but it's often an efficient thing to do, as long as you are aware of the limitations.