Property of the ScriptLine: BookFormat.
The Flow Direction property is used to determine if a diary is read from front-to-back (the Western way) or back-to-front (as is done for Arabic and Hebrew books).
the default front-to-back flow direction
the back-to-front flow direction
Flow of Dates in the GridTemplate
The Flow Direction setting reverses the order of appearance of 2-page layouts (hence preserving the symmetry of left and right pages), but it does not invert the sequence of DayValues within each page of a GridTemplate.
If you wish the dates within your grid pages to be reversed you must change the placement of tokens so that, for example, DayValues at the top left are 7, and those at the bottom right are 1.