Only people educated AFTER 1978 measure in Imperial! I was educated in both. I can comfortably work with both cm and inches. But …
Paper size and weight? Yeah. That’s still in Imperial. Ish.
Staples is the go-to for POD as far as I know. They do decent, inexpensive work for spiral type bound work. Nothing like perfect-edge finished “books” but they’re ok.
Well I feel better about using Staples now. I thought 37
CANADIAN dollars was a bit extravagant for a plastic spiral binding, but I'm still ahead of a commercial hardcover. Bolt Action 2nd Edition is $45USD, $60CAD, plus tax. I'll say the one advantage of a hardcover is that it looks better on your bookshelf. But then a spiral-binding is easier to hide in plain-sight from a spouse.