What are those diamond marks on steel tape measures

A selection of steel rulers designed for the UK andf US markets [click to see]Have you ever wondered what the strange diamond markings are that appear on steel flexible tape measures? They seem to be placed in an odd position, without explanation, somewhere near the 19” mark. Some tape measures have extra symbols placed at the 16” mark for some reason.

Most steel tape measures sold in the UK are made in China and are therefore sold on the USA market as well.

The diamond marks sometimes seen at 19.2”, 38.4” etc (i.e. every 19.2”) are for the UK market: in actual fact they enable tradesmen to accurately measure the centres of joists that will carry standard 8’ sheets of plywood, or maybe plasterboard.

Joists on 19.2" centres will carry an 8' board perfectly [click to see]Above I sketched how an 8’ sheet of ply will span six joists, if each one is centred every 19.2”. As five spaces measure 19.2” each, that totals up to 96” or 8’. (There are six telegraph poles, but only five 19.2" gaps, as my maths teacher might once have said.)

Something tells me metrication of modern materials has probably messed up this idea anyway.

My photo above shows a selection of steel tapes from my workshop. The centre one has a diamond at 19.2” for UK tradesmen, while some of them also carry black diamonds with numbers in a red box at [16]  [32]  [64]  [80]  etc – this is aimed at the US market instead, for measuring stud walls every 16”. Apparently the UK standard is 400mm centres instead, slightly different, so those marks are ignored. So now you know!