I don't have a good instinct for actual measurements based on pixels @ 96 dpi, so prefer to work with millimetres as my default unit of measure.
However, the ruler, when set to millimetres, bizarrely labels the ticks at 8, 16, 24, 32, etc. Most people working in millimetres expect major ticks at 10, 20, 20, etc. distances, with a larger tick at 5 mm and the smallest ticks at 2, 4, 6, etc.
At the moment I am using a grid on a background layer ruled in 2.5 mm intervals, so I would like the option to set the major tick labels and the subdivision ticks, e.g. in this case major labels at 10, 20, etc. and minor ticks at 2.5, 5, 7.5, 12.5, 15, etc.
I know ArtRage is intended as a freehand painting tool, but some of us want the texture effects plus some degree of precision when drawing art to fit a predetermined box in a publication layout.