what do the diamonds at 19"7/32 and at 38"13/32 and at 57"19/32 and so on, on a steel tape measure mean?. I was informed it was for old joist centres, however the diamonds are not uniformed in their spacings so i'm not sure about that?.
I don't know how to refer you directly to a webpage, still learning. However, try SEARCH -"how to read a tape measure", and you should get a site called asktooltalk. Hopefully your question will be answered. It was too complex to explain best of luck