Look at the rule before you measure anything with it.
01Look at the zero end of the rule before you use it.School rules are chipped, capped or worn. If the printed zero isn’t there, you can’t measure from it, and you won’t notice unless you look first.
02Lay the object flat against the rule, along the edge the scale is printed on.A scale printed away from the edge leaves a gap between the marks and the object, and you read across that gap at whatever angle your eye happens to be. Held against the marks, there’s no gap to misjudge.
03Line the near end up on a graduation you can see, 0.0 if the end is sound, otherwise any whole mark.Any mark will do. Starting at 10.0 measures exactly as well as starting at 0.0 and keeps you off the damaged wood.
04Read the near end, then the far end, with your eye directly above each mark in turn.Two readings, taken one at a time. Looking at the far end from where you read the near one puts your eye at a slant to it, and a slant is a parallax error.
05Subtract: length = final reading − initial reading.This is the step candidates skip when the near end is on zero, and then have no method when it isn’t.
06Write the answer to one decimal place in centimetres.The rule is divided in millimetres, so a tenth of a centimetre is the last figure it can justify. More places is a claim the instrument can’t support.