These Fischer and Bronstein modes have been hard to understand, let alone find on the Chronos chess clock. This video shows how to find the modes and explains what they mean.

FISCHER.  After a player has made his move, a specified time increment is added to his clock. Time can be accumulated, so if the player moves within the delay period, his remaining time actually increases. For example, if the delay time is five seconds, and a player has four seconds left on his clock, as soon as his opponent moves, he receives the increment and has nine seconds to make a move.  This variant prevents the player who is in time-trouble to take advantage of the extra-time.

BRONSTEIN. With the Bronstein timing method, the increment is always added after the move. But unlike Fischer, not always the maximum increment is added. If a player expends more than the specified increment, then the entire increment is added to the player's clock. But if a player has moved faster than the time increment, only the exact amount of time expended by the player is added. For example, if the delay is five seconds, the player has ten seconds left in his clock before his turn and during his turn he spends three seconds, after he presses the clock button to indicate the end of his turn, his clock increases by only three seconds (not five).

SIMPLE DELAY. When it becomes a player's turn to move, the clock waits for the delay period before starting to subtract from the player's remaining time. For example, if the delay is five seconds, the clock waits for five seconds before counting down. The time is not accumulated. If the player moves within the delay period, no time is subtracted from his remaining time. This time control is similar to a Bronstein with time added before the move.