Even in the days of mechanical move counters on the old BHB clocks, the scoresheet was the only tangible proof that the time control was made. Those move counters were notoriously unreliable, often moving only a partial rotation when the button was pressed. The clock might read 38 while you were on move 42. Sometimes if the clock was hit hard enough, the move counter would jump ahead a move or two. As a result, the clocks with move counters were not a popular seller. They are also a possible reason why rules were made to take account of the defect.
No, not yet anyway. Nevertheless, in a two-control tournament, if the clock is set to add time when move 40 (or whatever) is reached, then it’s still important that the move counter be correct. Otherwise, the clock may add time prematurely, which could (on some clocks, in some modes) mean that it will no longer be displaying minutes and seconds, but rather, hours and minutes. Not good if one or both players is short of time.
Example: White says, “I note that your move counter is not correct. It is showing two more moves than have actually been played.” Black replies, “Aw, never mind. We both know how many moves have been played. Let’s just play on. We both know that, if the displayed time goes under 1 hour before the counter says 42, then there has been a time forfeit.” Eventually it gets to the point where the counter says 41, and the players realize it is really 39, but one player’s time (because of the extra hour) reads 1:00, meaning 1 hour, 00 minutes, and an unknown number of seconds. The player may have 01 seconds left, or 59, to make his next move. Not a good pickle to be in.
I played on one of those once, and I hated it. The button on black’s side of the clock was extremely hard to press, due to the extra force necessary to advance the clumsy mechanical counter.
Bill Smythe
Please help me get my head around something that has been bothering me. Let’s say that the clock has a “move” counter and a player makes his 40th move adding time to his clock. But that move was an illegal move. How do you reset the clock back to the first time control since the player hasn’t actually made the 40th move once the clock thinks it’s in the second sudden death period?
This is just the same as with any other move. You have to set the move counter to 39, and anyway, you’re adding two minutes to the opponent’s clock. Again, the owner of the clock is supposed to know how.
Alex Relyea
I’m sorry, but that’s not quite right. If we were to reset the clock, we would also have to remove the added time in addition to resetting the move counter. Let’s say the time was 2:00 minutes before the key press and but the clock now reads 1:02 (the extra hour for the secondary control plus the previous 2 minutes). So if we reset the offender’s time back to 2 minutes and the move counter back to 39, will the hour be added again if the move counter goes to 40? Is the clock smart enough to know to do it again? What’s worse, as someone mentioned above, if there had been less than 1 minute left before the illegal move, on most clocks after the secondary time had been added it would not be possible to see how many seconds those were.
Jeez, now I have to get out my clocks and try it out and see what happens 
Sure. You’d set the clock either with 39 moves and 4 minutes, or set it for one move in four minutes, SD/60. No problem. I guess there are clocks on which it is possible to add and subtract time, but I was thinking of starting over. Let us know what your results are. I’m interested.
Alex Relyea
On the Chronos, for sure, you can do a mid-game time adjustment, and also a mid-game move-count adjustment.
Yes, in addition to changing the move counter from 40 back to 39, you’d also have to subtract the hour that was added – and also add two minutes to the clock of the aggrieved party. All very easy on the Chronos.
Let me know what happens on your Chronos – would it add yet another hour when the move count reaches 40 again? You try it on yours, I’ll try it on mine. (Mine is an old model, ca 1996.)
Bill Smythe
Amazing. I tried it on my new ZMF-II and it behaved properly. I simulated an illegal move on the part of black bumping the move counter and had time added. I restarted black’s clock (adding a move to white), stopped the clock, took away the added time from black, and reduced both move counter by one, and restarted black’s clock. When black’s clock was pressed, the move counter incremented and the additional time was added back. So at least this clock worked perfectly. Whew 
Funny, my old Chronos (ca 1996) behaves just the opposite. When I adjust the move counter back from 41 to 39, it does not add the hour when it passes move 40 again. Apparently the Chronos keeps track of whether time has already been added, so does not add again.
I’m not sure which is better. (I’m also not sure what more recent Chronos models would do.) If you adjust the move counter without thinking about its effect on the main time, you’re better off if the clock does not add again. But if you’re meticulous and do everything right, you’re better off the other way.
If the Smythe Dream Clock ever gets built, it would decide the issue based on total elapsed time rather than what’s on the display. Then, following a manual move counter adjustment, it would change the display according to what the counter now shows. In this example, it would automatically subtract the hour when the counter is set back to 39.
Bill Smythe
And then there are clocks programed to add the secondary time control only when the first one is used up AND the indicated number of moves have been made. This really throws players for a loop. They expect the time to be added when the proper move number has been added. We get several questions a round about that clock procedure.
Hmm, I’d never heard of that combination.
The Chronos, in its move-counter modes, adds time when the indicated number of moves has been made. In its non-counting modes, it adds when the first is used up.
I suppose, if halt-at-end is enabled, some clocks might freeze if the indicated number of moves has not been made when the first control expires.
Bill Smythe
I just tested the Excalibur Game Time II and it behaves like the Chronos. It does not add the hour when it passes the move number again. So so far, the ZMF is the only one that does it “right”.
Richard
– If that’s what you call “right”.
In my book, “right” would mean that, when you adjust the move counter backward past the time control, the time that had been added would be automatically subtracted. I doubt whether any clock presently on the market does this.
The same should be true of increment. With, for example, a 30-second increment, if it is discovered that the move counter is 3 moves ahead (e.g. on 29 when it should be on 26), and the move counter is then adjusted manually back (to 26), it should subtract the extra time that had been added (in this case 90 seconds).
Bill Smythe
That’s why I put “right” in quotes. Your suggested clock would be ideal, but I don’t see anyone producing one anytime soon.
Richard
It’s a simple matter of programming.
While you’re at it, add a button that returns the clock to its state just before the last clock press, removing all added time, reducing the move counter by one, and leaving the offending player’s clock running.
That’s HARDWARE. 