How far the blade extends horizontally before it buckles under its own weight. It is what allows one person to measure across a room or up to a ceiling without support, so a tape with poor standout effectively needs two people. It comes from the curvature across the blade, and it is a genuine differentiator between tapes.

By design, and by exactly its own thickness. Hooked over an edge it slides out; pushed against a surface it slides in, so both external and internal measurements read correctly from zero. A hook that has been riveted tight or bent by a drop introduces a constant error that is easy to miss.

They are formal tolerance classes under measuring instrument regulations, with Class I tighter than Class II. The class limits how far the tape may deviate over its length. For work that is charged for or built to, a classified tape is worth specifying, as unclassified tapes vary more than most users assume.

Push the tape into the opening so the hook bottoms out, read the blade, and add the case length, which is printed on the case for exactly this purpose. Forgetting the case length is the most common measuring error with a pocket tape, and it always makes the opening read smaller than it is.

A coating over the printed markings, most commonly nylon, which resists the abrasion that otherwise erases the first few centimetres and eventually the numbers. That first section takes the most wear because it is dragged over edges constantly, and it is where a tape usually becomes unusable first.

Wider blades give greater standout, which is the main practical benefit, at the cost of a bulkier case and more weight on the belt. For work involving long unsupported measurements the trade is usually worth it; for close bench work a narrower, lighter tape is more comfortable and easier to handle.

Compare several tapes against each other over their full length, or against a known reference, and check the hook by measuring the same distance internally and externally - a mismatch points to a damaged hook. Tapes on site get dropped and trodden on, and a bent hook is far more likely than blade error.