Don't Trust Your Tape Measure

Every once in a while on the woodworking forums there's a discussion about the problem of laying out and cutting parts accurately, and these talks typically tally time-tested tips like these:

1. Be careful!
2. Be sure to cut on the waste side of the line.
3. Use a knife instead of a pencil for marking.
4. Set up stop blocks for making repeated cuts.
5. Use relative dimensioning where possible.
6. Don't trust that sliding hook on the end of your tape measure.
7. And so on.

Here's one more tip:  For really accurate work, don't trust your tape measure at all.  Period.

"Really?" you say.  Well, yes.  As it turns out, the machine that makes tape measures uses a rubber belt to print the markings on the tape.  This belt can stretch slightly during the process, and when it does, the marks it puts on the tape will be misplaced by however much the belt stretched.  This means that while a particular tape may be perfectly accurate at, say, the 12-inch mark and the 24-inch mark, it might be off by a noticeable amount halfway in between.

Whether this potential inaccuracy actually matters or not depends on what you're doing.  In any case, though, it's a good thing to be aware of and something to think about if you're having trouble.  For much more detailed information, click here.