Fischer increments were officially recognized by the United States Chess Federation for tournament use starting in the mid 1990's. This caused a fair amount of contoversy at the time since players had to replace their analog clocks with (then more expensive) digital models. That initial furor has died down over time, but you'll see many players still using their analog clocks for casual "sudden death" games at chess clubs or between rounds at chess tournaments. (In fact, an analog clock is still my choice for "speed" games with my friends and family, since anyone can understand how to set and use one without any special instructions.)"  

In BrainKing we have 3 parts of Fischer's clock - A/B/C:
A - time for move (on the beginning of game)
B - time added after each move
C - maximum time for one move

Example #1 -> 30days/1day/30days

Games started at 8am. Your move at 9am
30 days - 1 hour + 1 day -> 30 days (because in C we have 30 days)

Example #2 -> 21days / 18hours / 31days 23 hours

Player X - dead time at 5pm, moved at 4:40pm (20 minuts before dead line)
20 minuts + 18 hours -> 18 hours 20 minuts