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What does the calibration number mean?

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What does the calibration number mean?

Old 10-27-20, 02:59 PM
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Metallifan33
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What does the calibration number mean?

So the manual of the Power2Max says it was calibrated at the factory and doesn't need to be re-calibrated.
I didn't know that a few days ago and calibrated it normally on my Edge530 and it said "calibrated successfully."
I did it again today and I got a failure.
I was wondering if you nice folk may have some insight for me. Is it something I need to worry about?
I guess I could put it on my tacx and compare the readings, but I was wondering what the significance of the calibration number is when the Edge 530 does its thing.
Thanks!


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Old 10-27-20, 03:04 PM
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What power meter? Call up that OEM tech support and tell them you keep getting that number for calibration. Sometimes it's a meaningless number but they can tell you for sure.
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Old 10-27-20, 03:18 PM
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Originally Posted by Psimet2001 View Post
What power meter? Call up that OEM tech support and tell them you keep getting that number for calibration. Sometimes it's a meaningless number but they can tell you for sure.
Cool. Thanks. It's a Power2Max, but the Garmin Edge provides a number regardless of the type of power meter and I was wondering what it meant. It doesn't have a unit or anything.
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Old 10-27-20, 05:03 PM
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Originally Posted by Metallifan33 View Post
Cool. Thanks. It's a Power2Max, but the Garmin Edge provides a number regardless of the type of power meter and I was wondering what it meant. It doesn't have a unit or anything.
I believe it's the factory calibration number your unit came with. These things are all calibrated before shipping. Could be Watts, I suppose. If you query the unit with the Power2max phone app, you can look up all the calibration stuff.
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Old 10-27-20, 05:39 PM
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Many head units use the term "calibration" to mean "tare" or "zero the torque value." When power meter manufacturers use the term "calibration" they mean to set the power meter's "slope calibration."

When you weigh yourself on a bathroom scale, you have to zero or tare the scale before you step on it so it knows where the zero is. That's what the Edge's "calibrate" function does. A different measurement is the slope or scale calibration, which sets how much the bathroom scale increases by for each pound (or kilogram) of additional weight. That's set at the factory, and you can't change it. Power2Max is talking about this latter type of calibration, and like a bathroom scale, you can't change it. Some power meters allow you to alter or change the slope calibration, P2M doesn't.

Either your Edge head unit isn't sending the right code to the P2M to initiate the zeroing, or there's a problem with the P2M responding to the request to zero. Turn the Edge off, let the P2M power down, count to 5, turn the Edge back on and wake up the P2M, and try again. In years past computers and head units were much less powerful than today, so we used to have to count to 10.
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Old 10-27-20, 06:16 PM
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P2M may use negatives as error codes. I have more experience with Quarq, where failures don't return a number and can be almost literally whatever. For example, the Dfour91 on my roadie is usually in the mid-30s (34 last time) while the Dzero on my P2 is usually -300 or so. Both return accurate power.

Tech support time though, yes.
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Old 10-27-20, 08:23 PM
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From the P2M FAQ page:

HOW CAN I CALIBRATE MY POWER2MAX MYSELF?

There are two important values for the precision of crank-based power meters: zero-offset and slope. The zero-offset is the value that the power meter reports when there is no torque, i.e. when you are not pedaling and there is no tension on the chain. The slope indicates how much the measured value changes as torque increases.

power2max power meters automatically update the zero offset when you stop pedaling. Anytime you stop pedaling long enough (approximately 3 seconds or more) power2max updates the zero offset. You can also update the zero offset manually through a compatible head unit.

The slope does not need to be calibrated by the user. Other systems require calibration in two cases:

1. When you change chain rings 2. Due to aging of the materials of the power meter

power2max power meters have been designed in such a way that you can change chain rings without having to recalibrate the unit. Calibration remains unaffected by the choice of chain rings and chain bolt torque. We do however, recommend tightening chain bolts to the prescribed torque.

Furthermore we have constructed power2max power meters in a way that aging of materials is not an issue. You don't have to worry about the calibration of your power2max.

If you want to verify the calibration of your power meter anyway you can send it in for calibration. However, we don't see this as necessary.

Another possibility is to conduct a dynamic calibration yourself: you can compare the values from your power2max with a CYCLUS 2 professional ergometer. This ergometer also has a known precision of ±2%. Please contact us for a comparison test protocol if you wish to conduct this test.
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Old 10-28-20, 07:45 AM
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Originally Posted by DrIsotope View Post

From the P2M FAQ page: [...] You can also update the zero offset manually through a compatible head unit.

Yeah, P2M is a pretty good power meter, but they like to claim that it's impossible for end-users to check their accuracy and precision without special tools and procedures that only they know about: "Just trust us." Stages used to make the same claim.
The manual setting of zero-offset is what the Garmin head units do when you "calibrate" a power meter.

Last edited by RChung; 10-28-20 at 07:49 AM.
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Old 10-28-20, 12:00 PM
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I've owned several P2M meters, including one of their Track units (which had the auto zero disabled). As others have stated that is just a zero offset although I've never seen that error statement. Send an email to Power2Max they are very responsive and will usually get back to you within a day.
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Old 10-31-20, 10:21 AM
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Originally Posted by RChung View Post
Yeah, P2M is a pretty good power meter, but they like to claim that it's impossible for end-users to check their accuracy and precision without special tools and procedures that only they know about: "Just trust us." Stages used to make the same claim.
The manual setting of zero-offset is what the Garmin head units do when you "calibrate" a power meter.
Originally Posted by Voodoo76 View Post
I've owned several P2M meters, including one of their Track units (which had the auto zero disabled). As others have stated that is just a zero offset although I've never seen that error statement. Send an email to Power2Max they are very responsive and will usually get back to you within a day.
Ok, I ended up resetting the Garmin 530 and repairing it and everything zeros out perfectly now. The P2M has been great. The only issue I had is if I'm trying to pair it using ANT+ and it is connected to my phone via bluetooth.
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Old 11-02-20, 10:05 AM
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Originally Posted by Metallifan33 View Post
The only issue I had is if I'm trying to pair it using ANT+ and it is connected to my phone via bluetooth.
There shouldn't be any issue with that. The only issue is Bluetooth can only pair to one device at a time. ANT+ can pair to multiple devices. Maybe you thought it was connected via ANT to one device when it was actually connected via Bluetooth.
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Old 11-02-20, 10:17 AM
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Originally Posted by jadocs View Post
There shouldn't be any issue with that. The only issue is Bluetooth can only pair to one device at a time. ANT+ can pair to multiple devices. Maybe you thought it was connected via ANT to one device when it was actually connected via Bluetooth.
Huh... I just checked and you are right. Even though I thought I was connecting to the Edge 530 via ANT+, it was actually bluetooth. Interesting because nothing else comes up when I try to pair. Is there one reason or another that I should pair a PM with Ant+ as opposed to BLE? I know that BLE gives me additional data (such as torque), but I thought ANT+ was a more stable connection and uses less battery.
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Old 11-02-20, 12:21 PM
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Originally Posted by Metallifan33 View Post
Huh... I just checked and you are right. Even though I thought I was connecting to the Edge 530 via ANT+, it was actually bluetooth. Interesting because nothing else comes up when I try to pair. Is there one reason or another that I should pair a PM with Ant+ as opposed to BLE? I know that BLE gives me additional data (such as torque), but I thought ANT+ was a more stable connection and uses less battery.
Huh...I don't use Garmin products so I can't speak for the head unit. On the other hand my PM connects to my Wahoo via ANT. I'm not sure if there is some kind of protocol these head units have such as.... always looking for a ANT signal first then if there is none defaulting to BTLE. In your case though you said it is connected via BTLE...Out of curiosity, how far away was your head unit when you paired it? I'm just thinking out loud as to why your Garmin has defaulted to BTLE.

I believe a BTLE connection is going to be more stable since it has more range, but I could be wrong. My experience with ANT+ is I need to keep everything within 3 feet or 1 meter, otherwise your dealing with dropped connections. I can't speak to battery life as I have never compared the two.
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