The grid on the screen is not a ruler
A page preview changes size to fit your phone or monitor. Its squares therefore cannot tell you the physical spacing of the printed paper. The PDF stores that spacing in document coordinates: a 5 mm interval stays 5 mm when the printer uses the original page size at 100% scale. A print dialog set to Fit can quietly shrink the entire page, including the grid.
Start with one proof sheet. The optional line in the bottom margin should measure 50 mm between its end ticks. If it measures less or more, check the selected paper size and print scaling before changing the grid settings. A printer may reserve nonprintable space around its edges. The minimum 10 mm margin gives the grid some room, but it does not guarantee every printer can reproduce the same page.
Square grids are useful for tables, measurements and sketches. Dots give similar alignment cues with less continuous ink on the page, while ruled lines leave horizontal space for handwriting. The generator does not infer an engineering drawing scale from grid spacing. If five millimeters on paper represents one meter on site, record that scale separately and verify it against your drawing requirements.
Binding allowance shifts the usable area inward without changing the spacing. Alternating the allowance moves it from left to right on successive pages. Check your printer’s duplex flip setting with a two-page proof, particularly in landscape orientation. Page count creates repeated pages inside one PDF; it is separate from the number of copies requested by a printer. Use the printing-cost calculator with the generated PDF to estimate supplies for the actual job.