The number of major divisions within each primary grid cell.
This is the number of major divisions per interval, including the primary grid's line.
The lines after the first are half a logical pixel wide.
If this is set to 2 (the default), then for each interval there will be a 1-pixel line on the left, a half-pixel line in the middle, and a 1-pixel line on the right (the latter being the 1-pixel line on the left of the next interval).
final int divisions