I built a tiny tool that catches the "printed at 94%" problem

Hi everyone,

I built a free print scale checker as part of my printer test site, after running into a frustrating problem: prints that look fine but come out the wrong size.

The usual cause: an A4 file printed on Letter with "Fit to page" on shrinks to about 94%. Nothing looks broken, but templates, labels and patterns are off.

What I focused on:

• Print one sheet, measure a 100 mm bar, type the number
• It tells you the scale and whether it matches a paper-size mismatch
• Runs in the browser, nothing uploaded

What I learned:

• "The printer printed" and "it printed correctly" are different checks
• Real vector PDFs beat HTML print for exact sizes

Question for developers: have you built anything that has to print at an exact size? How did you test it?