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This means is that the clock has two serious design flaws:
Digital chess clocks must not mistake their clock-punch counter for a move counter: it is not a move counter.
The time control used in a typical tournament game consists of a sequence of segments. For example, the time control “40moves/90minutes, SuddenDeath/60minutes” has two segments.
Digital chess clocks need to display two segment counters, one for each player. The segment counter for one player has no effect on the segment counter for the other player.
The individual player’s clock should suddenly add the time for the next segment --when but only when-- its time ticks all the way down to zero. The segment counter should not be affected by the clock-punch counter.
The clock must display the segment number that the player’s clock has reached.
I do not believe that most digital chess clocks do this today. When you peel the onion to its core, this combination of 1 & 2 is the only way that White can ascertain that Black has suffered flag fall, without requiring White to keep track of Black’s time over a span of moves. (Granted the tracking that White must do of Black’s time usage is truly minimal, but it is more than nothing, so a principle is kinda violated.)
I can detect the fall of my opponent’s flag only by…
(A) Seeing that his clock says segment #2 when my trusted score sheet says he has not completed enough moves to satisfy segment #1; or
(B) Seeing his clock hold still at a value of zero time remaining; which must mean the end of the final segment that is a sudden death style segment (no more segments to follow).
For any digital chess clock that ticks its time down to zero…
- A clock that lets its clock-punch counter have any effect on any other display aspect is flawed.
- A clock that does not display the current segment number, separately for each player, is flawed.
- A clock that does not increment its segment counters in the correct circumstance (as described above), is flawed.
Analog dial clocks, with a big hand for the minute and a little hand for the hour, do implicitly display the current segment number, separately for each player. This is because they tick their time UP not DOWN. For example…
Suppose the two segment time control is “40moves/90minutes, SuddenDeath/60minutes”.
If the game started with both clocks set to 2:30, and now my opponent’s clock reads 4:01, I know his time control has advanced to its second segment. If my score sheet shows my opponent has made less than 40 moves I can declare him in flag fall.
A digital clock could also tick its time display UP I guess. Maybe some do?
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