Guides to the parts that aren't the grid itself. Making your printer produce true-size output, choosing paper that suits your pen, and getting cell proportions right so a chart turns out the way you drew it.
Print dialogs scale pages to about 94% by default, so 5 mm squares come out 4.7 mm. What causes it, and how to check what your printer did.
Knit stitches are wider than they are tall. Charting on square graph paper flattens the design. Here is how to get the proportion right.
Heavier paper is not automatically better for fountain pens. Why 90 gsm Rhodia outperforms 120 gsm cardstock, and what to print grids on.