A backgammon clock needs a delay time option, to roll the dice and make the move, called free time. The clock also needs a countdown option, additional limited time which can be used for thinking, called the reserve time. The backgammon clocks in this category have those features. Note: the Bronstein delay time option is not suitable for backgammon.
For Backgammon there are two time limits. One is the free time per move, to roll the dice. The other is the reserve time. A player's reserve time is not touched unless he overshoots his free time per move. For example, suppose the time limit is 12 seconds per move with a reserve time of 15 minutes. If a player makes his move in under 12 seconds, his reserve time remains the same. But if he takes 25 seconds to make his move, then 13 seconds will be deducted from his reserve time. Most plays will be routinely made in 12 seconds, so this is a good setting for the free time. Per game 2 minutes is a good reserve time, normally with an additional minute. So for a 7 game match 15 minutes is a good reserve time.