switching counters in the middle of a measurement

That's a good question. It would be a good experiment for one to try.

There's no need to recalibrate after switching counters. The wheel itself remains unchanged.

The only thing to look out for is to be sure both counters record 23.636363 counts per revolution. Some of the pre-JR dinosaurs record 20 counts per revolution of the wheel, while modern counters record 23.6363636.. counts per revolution.

In this unlikely event, only bit of figuring is needed, not a recalibration.

I wonder what the Measurement Data Sheet and the Calibration Data Sheet would look like if counters were switched. Especially if the measurement started using a dinosaur and switched to a JR.

I had that exact issue when measuring Twin Cities a few years ago. Fortunately I'd brought a second counter; unfortunately it was a different model (but at least I knew right off the bat the counts would differ); fortunately I'd followed Pete's advice to measure in segments so I didn't have to redo the whole ride.

Mark,

Can you share what model this was and what the trouble was?

Interesting discussion.

Sure Bob. The counter was the new JR model, but that actually turned out to be irrelevant. I started having the situation where the counter itself started rotating around the axle until it would go all the way around and bump into the fork. At this point it was facing down.

It seemed to be binding the wheel so that the wheel would not spin freely. After much fiddling I finally just took the counter off(not the first thing you think of doing when you're in the middle of a measurement) and discovered that the wheel still didn't spin freely. It turns out the axle was bad. I muddled through that day, and when I got home I bought a new wheel, and everything works great. My troubles had nothing to do with the counter.

But I'm still interested in my original question. If you do have a counter failure in the middle of a measurement, is it okay to replace it without recalibrating? Pete is exactly right that a new counter shouldn't have any effect on the calibration. But I think we all have the mindset that once you calibrate you don't want to change anything. I'm nervous even about taking my front wheel off and putting it back on. So even though it makes sense that changing a counter is not going to effect the calibration, it's something I would want to test out before actually doing it in the field in the middle of a measurement.

I can identify with that feeling, I don't like to take off my front wheel either. But I think this may be one of those times when we should allow logic to overrule those "gut feelings."

I asked about counter model etc because I had some problems with lots of noise with my new counters. I'm not sure why it occurs but whenever the counter starts to get noisy I put oil on both sides of the drive wheel for the counter, and that quietens it up.