extend the grid interval from 377.7 mm to 1000 mm (or more who cares if it 100,000,000 with 1000 subdivisions?)
to make it easier to use real world dimensions when drawing large artwork in AI I have a document that is a few metres wide and a few metres high.
I want the major grid lines at 1000 mm interval (its a 1 to 1 technical drawing) and subdivisions of 10, so minor grid lines at 100 mm intervals.
I can't, AI has a max grid interval of 377.777777.
Doesn't make sense to limit it in this way. Grid intervals in AutoCAD etc are whatever you want them to be at all.
Alastair Leith commented
Also there's an associated bug.
when you change the document's unit of measure from metres to millimetres by right-clicking in the ruler, this change is not reflected in the info Window. Even if we close the info window and open it again. (macOS Ventura AI v2023)