Question: Open Class - chrono hand advanced 0.5sec when started

[siukei]

Hi,

Just bought the new Open Class.

I noticed when I start the stopwatch, the chrono hand start to tick. When I stop it and restart it again, I find the hand advances about 0.5 sec before it move smoothly.

For timing wise, it seems ok as it seems to be waiting for about 0.5 after the 0.5 advancement (to compensate??) I tested it to stop and start for many time without reset along with a CASIO, seems the timing is not affected even thought the accumulated of the many 0.5sec advancement.

Is it as designed for Zentih's El Primero movement? If so, why?

Skei

[D N Ravenna]

Hello Skei,

That is fairly common in many chronographs. About the few that do not seem to be affected are those like the Omega using the Broadarrow movement. But Zenith, Rolex, IWC, and many others show this symptom. It is not a sign that something is wrong.

Hope that helps!

Dan

[Hartmut Richter]

The reason for this is the way that the chronograph second hand interacts with the permanent second hand. When the chrono starts, the intermediate wheel is jammed onto both to connect the two. If tooth hits gap, everything goes all right. If tooth hits tooth, the chronograph second hand is forced slightly backward, causing a delay, or forward, causing a jump which is what you are complaining about. All chronographs with a so-called horizontal clutch have this (although from what I read, the Valjoux 7750 is not so badly affected - anyone out there can verify this?!). The only way around it is the vertical clutch, first invented by Pierce in the fifties and adopted & perfected by Frederic Piguet in their Cal 1185 and since then copied by other makers in their new chronograph movements (most notably Rolex and Jaeger LeCoultre).

Hartmut Richter

[siukei]

The reason for this is the way that the chronograph second hand interacts with the permanent second hand. When the chrono starts, the intermediate wheel is jammed onto both to connect the two. If tooth hits gap, everything goes all right. If tooth hits tooth, the chronograph second hand is forced slightly backward, causing a delay, or forward, causing a jump which is what you are complaining about. All chronographs with a so-called horizontal clutch have this (although from what I read, the Valjoux 7750 is not so badly affected - anyone out there can verify this?!). The only way around it is the vertical clutch, first invented by Pierce in the fifties and adopted & perfected by Frederic Piguet in their Cal 1185 and since then copied by other makers in their new chronograph movements (most notably Rolex and Jaeger LeCoultre).

Hartmut Richter

Thanks, Hartmut,

a very knowledgeable explanation.

You're right, I check my current Daytona, it doesn't have the "jump" problem.