Found this gem of an item on eBay, an A4-size graphing paper
Oxford Computer Graphics Pad
ZX Spectrum
ZX 80/81
At first I thought it was merely a branded notebook, with a Sinclair theme. But then I realized it matches the screen resolution when used in horizontal orientation
I could have used this last year when I was deciphering the mechanics of a hi-res game, i recreated something similar from scratch
A: 32x24 characters
B: PLOT characters
C: 256x192 (8x8-pixel characters)