The digital chess clocks belonging to the Bonus-Only category differ from the timers in the Entry Level category by functioning solely in a count-down game mode for one time period with bonus (Fischer increment) capability. The timers in this category do not offer count-up functionality, nor do they provide the extra delay functionality of the higher ranking Bonus-Delay category timers.
With the bonus option activated for these timers each player is allocated an amount of extra time before each move, configurable for one time period. Named after the late world champion Bobby Fischer who advanced the concept, it helps to minimise time scrambles marring competitive play.
The Bonus-Only category timers are suitable either for players requiring bonus capability for one time period or for players who while not presently having this need, are attracted to the potential flexibility for a small premium over an Entry Level category timer in the count-down game mode.