@Pete,

I'll give it a try.
I scanned through my PBP3 manual and could not find "MOD" anywhere. It doesn't show in the reserved word list either.

From the link that Pedja089 posted...
USA starting in 2007, extended DST to
begin on the 2nd Sunday in March (Day of month = 14 - (1+Y*5/4) mod 7)
and end on the 1st Sunday in November (Day of month = 7 - (1 + 5*Y/4) mod 7).

For Europe...
DST begins on the last Sunday in March (Day of month = 31 - (4+ 5*Y/4 ) mod 7)
and ends on the last Sunday in October (Day of month = 31 - (1 + 5*Y/4) mod 7)