Those black diamonds are the cubit marks. You remember the story of God and Moses and the Ark? The cubit is God's pwesonal measure ment system and is based on the length of the forearm. When Horatio Stanley, a very devout Christian, invented the tape measure in 1926, he included these cubit marks just in case someone might need to build another ark. It so happens that an 8' plywood or gypsum board panel divided by 8 os exactly equal to 19.2" which is pretty close to 19 3/16ths". This has proved useful in construction since it provides more joists that 2' on center but less than the traditional 16" on center. ~Peter
Pete I think someone has been pulling your Christin leg.
From Stanley Tools knowledge base.
The black diamond marks every 19.2" on our tape rule blades are for spacing joists and studs. Several wood product manufacturers offer Engineered Lumber as a substitute for conventional lumber. Span tables for these lumber products provide ratings for spacing of 12in., 16in., 19-3/16in., and 24in. If you multiply these dimensions by 8, 6, 5 and 4, respectively, you'll notice that you come up with 96in., the length of the panels that will be used for sub-flooring or sheathing. Engineered Lumber is usually specified by the architects and engineers who draw the plans. They take advantage of its strength by using fewer joists or studs where codes allow.
No mention of a cubit.
I did find that 'cubits' range from 16 to 26 inches depending on who is doing the measuring.
Bob Badger Construction & Maintenance Electrician Massachusetts
5 joist or stud layout alternative to 24"(4), or 16"(6) per 8' (Most logical answer)
Truss layout (Not mentioned here)
And the "Stanley Cubit" (Pete was not alone on this, there are many who prescribe to the same therory. *More on this in a minute...)
My favorite so far, and related to the one above. "It's a Masonic Order thing... You wouldn't understand."
*Asked around to a bunch of old framers who note that it must have been around for some time, because they only ever see this lay out used in baloon frames in the early 1900's and prior. Well before plywood and sheet-rock, back when '2X4's' were 2X4".
Anyway, at this point, I think this is a Myth Busters Issue.
Mark Heller "Well - I oughta....." -Jackie Gleason