Rule 8 of 31 · Chapter II — Measure and Mark

Use one tape for the whole project

Why this rule exists

Here's a gotcha that bites beginners: two tape measures don't always agree. The hook on the end is meant to slide exactly one hook's-thickness to read true for inside and outside measures, but tapes vary, and bent hooks make it worse. Measure a part with one tape and its mate with another and you can be off enough to matter. Sticking to a single tape keeps any small error consistent, so parts still match each other.

In practice

Pick one tape and marry it to the project for the whole duration, then set the others aside. If you and a helper are both measuring, use the same tape or first check that both read identically against a known ruler. Better yet, for repeat parts, ditch measuring altogether and use a story stick or stop block. When you buy a new tape, test it against your trusted rule before you rely on it, since a fresh one can be just as off as an old one.

When it doesn't apply

For independent tasks that don't need to match each other, like cutting shelves to fit separate spaces, any accurate tape is fine. The consistency matters only within a set of parts that must relate. And if all your tapes are verified against one standard, they're interchangeable.