Which measuring tools do I need for accurate work?

Measuring tools are where accuracy enters or leaves a job, and they are the category people economise on because the difference is invisible in the shop and obvious in the finished work.

Step by step

1. Buy a decent tape measure.5m or 8m, a wide blade that stands out unsupported, a clear scale and a hook that moves. Cheap tapes have vague printing and a loose hook, and they read differently pushed and pulled.
2. Understand the moving hook.It slides by exactly the hook's thickness so internal and external measurements both read true. It is meant to move, and people frequently think it is broken and try to fix it.
3. Use one tape for a whole job.Tapes disagree by a millimetre or two. Mixing them across one job introduces errors that look like your own mistakes.
4. Buy a proper combination square.The single most useful marking tool: 90 and 45 degrees, an adjustable depth gauge and a straight edge. Spend here rather than on a fixed try square.
5. Test any square before trusting it.Mark a line across a board with the square against a straight edge, then flip the square over and mark again from the same point. Two lines that diverge mean the square is out. Cheap squares fail this routinely.
6. Get a marking knife rather than relying on a pencil.A knife line is far finer than a pencil line and it gives the saw or chisel something to register in. It is the cheapest accuracy improvement available in woodwork.
7. Keep a sharp pencil for rough work.A carpenter's pencil sharpened to a chisel point, or a fine mechanical pencil. A blunt pencil line is a millimetre wide, which is more than most tolerances.
8. Add a long straight edge.A metre or more of aluminium, checked straight. For marking long cuts, checking flatness and bridging spans that a level cannot cover.
9. Consider a digital caliper for small work.Inexpensive now and the only sensible way to measure thicknesses, dowel diameters and small internal dimensions. Worth having if you do any fine work.
10. Add a sliding bevel for angles.It copies an existing angle and transfers it, which matters because corners are rarely 90 degrees. Essential for skirting, architrave and anything in an old house.
11. Measure from one datum, not cumulatively.Mark everything from a single reference point rather than measuring from each mark to the next. Cumulative measuring accumulates every small error along the run.
12. Use a story stick for repeats.A batten marked with the positions, used to transfer them directly. It removes reading errors entirely and is faster than measuring each one.
13. Look after them.Squares knocked off a bench go out of true. Tapes with a kinked blade read short. Keep them somewhere they are not being buried under heavier tools.

Tips

• Test the square with the flip-over line test before you use it. Cheap squares fail it far more often than people expect.
• One tape per job. Two tapes disagreeing by a millimetre produce errors that look like carelessness.
• Mark everything from one datum. Measuring mark-to-mark accumulates error along the whole run.

Common mistakes

• Assuming a square is square — Cheap squares frequently are not, and everything marked from one inherits the error. Test it with the flip-over line test first.
• Trying to fix the moving hook on a tape — It slides deliberately, by exactly its own thickness, so internal and external measurements both read true. Fixing it makes every measurement wrong.

If it doesn't work

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