Tony, Each Fuso (time zone) has a Zonal Designation (a letter) and a Zonal Correction, to get the UT. The time zone Z has the Zero Meridian (Greenwich) in the middle, is called Zulu, and has for Correction 0. to East to West A -1 G -7 N +1 T +7 B -2 H -8 O +2 U +8 C -3 I -9 P +3 V +9 D -4 K -10 Q +4 W +10 E -5 L -11 R +5 X +11 F -6 M -12 S +6 Y +12 M and Y are the same Fuso and it contains the Change of Day Line (not a straight line, because of Alaska and some Pacific Islands). jorge