Books that state their own measurements.

Almost no notebook seller states its ruling pitch. They write "lined" or "dotted" and stop there, so the only way to find out whether your handwriting fits is to buy one first.

These books come off an engine that knows its own geometry, so every product page states the figures: the pitch in millimetres and points, how many rows that yields at this trim, the signature count, and the spine thickness. The same numbers are printed on the last leaf of the book itself.

One ruling gives different line counts at different sizes. College ruling at 7.14 mm gives 24 lines on A5 and 21 on 5 × 7 inches. That is not a small detail if you write by hand every day.