Measure twice: using a tape measure and a level properly

Measuring a wall with a tape and painter's tape mark
Kelvin Tools

Every Kelvin folding multitool carries a tape measure and a liquid level, because they are the two measurements that decide whether a job looks right. They are also the two tools people assume they already know how to use.

The tape

The hook is supposed to move

The metal hook on the end slides by exactly its own thickness. Hooked over an edge it pulls out; pushed against a wall it pushes in. Either way the reading is correct. Do not bend it back.

Read from the same edge every time

Pick the top edge of the blade for every mark. Switching edges between marks adds a millimetre of error that becomes visible on a shelf.

Burn an inch when precision matters

For a cut or a bracket spacing where a millimetre counts, start the measurement at the 1-inch (or 10 cm) mark and subtract. It removes the hook from the equation.

Know your length

The Kelvin 17 carries a 3 ft (1 m) tape, which is enough for frames, shelves and furniture. The Kelvin 23, 36 and 36 SL carry 6 ft (1.8 m), which reaches sofa and doorway questions in one pull.

The level

A level is only as true as its length

A short bubble level reads the surface it sits on, not the whole span. For a long shelf, set the level on the shelf itself, or on a straight board laid across the brackets.

Check the level against itself

Set it on a surface, note the bubble, then turn it end for end. If the bubble sits in the same place, the level is true. If it moves, split the difference.

Level across, do not measure twice

When two points need to be level, mark the first, then hold the level from that mark across to the second and mark where the bubble centres. Two separate height measurements multiply the error.

Plumb is level turned sideways

Door frames, bookcase sides and tall mirrors want to be plumb (vertical). Hold the level against the vertical edge and read the end bubble, or on a multitool, simply turn the body.

The combination

Tape to find the position, pencil on painter's tape to mark it, level to confirm it, then the screwdriver arm to fix it. On a Kelvin that is one tool in one hand, which is the whole point.

Compare tape lengths and tools

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