Torn skin reveal with square and compass on upper arm

I went to the reunion after all, though I stood by the urn of stewed tea for most of it, counting who had gone grey. Mr Pryor was there, or what remains of him in a wheelchair with a mackintosh over his knees. He asked after you. I said you were still drawing things nobody asks for, which is true, and he laughed the way he used to when we got an angle wrong in technical drawing.

Then the caretaker, Dennis, handed me a flat parcel in brown paper that had come out of the old drawing office when they gutted it. Inside was a sheet of cartridge paper, foxed at the corners, with a ruled square and a pair of dividers pinned over it like two crows on a fence. Someone had drawn an eye at the apex, then torn the paper away around it in ragged strips, as if the design had been hiding under a skin of ordinary sheet all along.

I think it was Pryor's. I think he drew it the summer before he retired and never showed anyone, because the pupils would have laughed. Under the eye, in pencil so faint I had to tilt it to the window, he'd written: measure twice, cut once. And beneath that, a line I can't make out at all.

I've enclosed a photocopy. Come and tell me what it says, or come and tell me I'm being daft. Either will do. The tea is still terrible.

Love, Margaret