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Presets set the mode, starting time, and increment or delay.
The selected rule is frozen when the clock starts.
0–600 whole minutes.
min
0–59 whole seconds.
s
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Up to 40 characters.
Up to 40 characters.
This side runs first after Start or Reset.
Use 0 to disable the warning.
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Off by default for quiet play.
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Controls only the optional local tones.
SidePlayerClockMovesStateCopy
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#EventSideWhiteBlackDetailCopy
{{ row.number }}{{ row.event }}{{ row.side }}{{ row.white_clock }}{{ row.black_clock }}{{ row.detail }}

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A chess clock divides one shared game into two separate time budgets. Only the player on move spends time, and pressing the clock after moving transfers the running clock to the opponent. That handoff makes clock handling part of play: thinking, moving the piece, and completing the press all use the active player's allowance.

The familiar notation 5+3 is incomplete unless the three-second rule is named. With Fischer increment, three seconds are added after every completed move and can accumulate. With simple delay, the main clock does not fall during the first three seconds of a turn. Bronstein delay shows elapsed time during the move, then refunds up to three seconds when the clock is pressed. These controls can begin with the same display and produce different balances after only a few moves.

Mode What happens during a turn Can unused bonus time accumulate?
Simple countdown Every elapsed second reduces the active clock. No
Fischer increment Elapsed time is charged, then a fixed increment is added after a completed move. Yes
Bronstein delay Elapsed time is charged, then used time is refunded up to the delay limit. No
Simple delay Main time begins falling only after the delay expires. No

Short controls put more weight on clean handoffs and quick decisions. Longer controls leave more room for calculation, while increment or delay reduces the chance that one awkward move consumes the entire reserve. Category names such as bullet, blitz, and rapid vary by organizer, so the actual agreement is the base time, the per-move rule, and any event-specific flag procedure.

Reaching zero is a timing fact, not a complete chess ruling. Checkmate, drawn positions, claims, equipment defects, and tournament procedures can still determine the result. Casual browser timing is useful for practice and informal games; rated events should use the organizer's approved clock and rules.

How to Use This Tool:

Agree on the time rule before the first move, then keep every press aligned with the player who just moved.

  1. Choose a Time control preset, or select Custom and enter the starting minutes, starting seconds, and increment or delay. The total starting time must be above zero.
  2. Select the Clock mode, enter player names, and confirm the First side to move. A preset fills the mode and timing values, but the chosen rule is frozen only when play starts.
  3. Set Low-time warning only if a visible warning is useful. A value of 0 disables it, and the threshold changes no clock arithmetic.
  4. Press Start, then press the active clock face or Switch after each completed move. Use Pause for an agreed interruption; Reset clears the session and reloads the editable setup.

Interpreting Results:

The active clock is the one currently spending time. A low-time state begins when a nonzero warning threshold is reached or crossed. A flag records that the running clock reached zero and stops the session; apply the chess rules in use before assigning a game result.

The move ledger records starts, switches, pauses, resets, and flags. The balance chart connects those event points, so it is useful for comparing time after handoffs but is not a continuous trace of every fraction of a second. Under Fischer increment, a player can rise above the original starting time, so time spent relative to the starting balance can remain zero even after several quick moves.

The setup and run stay in the browser, with no game record uploaded for calculation. Browser timing, sound, and device performance are still unsuitable substitutes for approved tournament equipment.

Technical Details:

Each turn begins with a stored balance and an elapsed-time counter. Simple countdown, Fischer increment, and Bronstein delay show elapsed time reducing the active balance while the turn runs. Simple delay subtracts only the portion beyond its protected opening interval. A completed press commits the active balance before any Fischer increment or Bronstein refund is applied.

Formula Core:

Let m be starting minutes, s starting seconds, R the balance at the beginning of a turn, e elapsed turn time, and b the selected increment or delay, all in seconds.

R0 = 60m + s

For simple countdown, the live balance is the turn-opening balance minus elapsed time, bounded at zero.

Rlive = max(0,R-e)

A Fischer press adds the full increment after elapsed time is charged. A player who reaches zero before pressing flags and receives no increment.

Rnext = R-e+b when e<R

Bronstein delay refunds only the time actually used, up to the delay. Simple delay produces the same nonnegative charge for a completed turn, although the live display behaves differently.

Rnext = R - max(0,e-b)

Rule Core:

Rule Exact behavior
Starting time 0 to 600 whole minutes plus 0 to 59 whole seconds; their combined value must exceed 0 seconds.
Increment or delay 0 to 120 whole seconds. Simple countdown applies 0 seconds even when a value is entered.
Low-time warning 0 to 600 whole seconds. A positive threshold is active at remaining time less than or equal to that value.
Flag order Zero is checked before Fischer increment or Bronstein refund is awarded on a press.
Display precision Whole seconds are rounded upward; the active clock shows tenths below 10 seconds.

Starting a game freezes the mode, timing values, starting side, names, warning level, and tone settings. Later form edits do not rewrite the active session.

Worked Examples:

Four-second move from a 5:00 balance

With a 3-second Fischer increment, the next balance is 4:59. With a 3-second Bronstein delay or simple delay, it is 4:59 as well. The totals match for this move, but Fischer would show 5:02 after a one-second move while either delay mode would return to 5:00.

Delay cannot rescue a flag

A player with 2 seconds left who takes 2 seconds before pressing reaches zero. In Bronstein mode the flag check happens before any refund, so the session stops instead of restoring delay time.

References: