Good question
I think there is just the annual requirement. There is the 7 in 28 and average 8 in 3 x28 day periods for 'days off'. But days off include G, O and A days. The reason it was 92(now 102) was to allow for not getting any G's over leave period (52 -6 weeks leave=46 weeks work. 2days off a weekx46=92 G days)
clear as mud?