Did anybody successfully calibrate HRM-Pro manually?

I find the pace from HRM Pro useless despite following the calibration steps.  Always out by around 30-40 seconds per mile. 

forums.garmin.com/.../pace-discrepancy-when-using-hrm-pro-for-pace

Are you using 10.43? This has some bug fixes for HRM pace. 

Yes, including the 10:43 beta beforehand. 

Calibrating the Treadmill manually is useless for the HRM-Pro use. You only need to calibrate it by GPS runs. Attempt to run in good GPS conditions - flat terrain, open space, good visibility to the entire sky, and with your standard pace.

Keep the HRM-Pro setting always on the option "indoor", do not use the option "always"! It will still improve the accuracy of your outdoors GPS runs anyway, because each such run is a mixture of outdoor and indoor sections. The more track points with low GPS accuracy the activity contains, the more the "indoor" mode is used. When no HRM-Pro is connected (or when it the HRM-Pro distance option is disabled), the distance data comes from the watch's accelerometer + gyro, and it is typically very inaccurate. 

The distance (and consequently also the pace) at my running activities, when not using HRM-Pro, are typically underreported by 10%, while when using the strap, they are within 1% of the known distance (more often rather ~0.5%).

Just to be sure if I have understood you well. You use the HRM-Pro with the option indoor,  running outdoors and it improves the distance accuracy?.

Another doubt I suppose you set it to always to do the calibration.

Mine always underestimates the distance but I want to try calibrating it again.

AlbertoGaMo said:

Just to be sure if I have understood you well. You use the HRM-Pro with the option indoor,  running outdoors and it improves the distance accuracy?.

Yes, exactly. As I wrote, the "indoor" calibration mode is in fact used also at outdoor GPS activities as well, whenever the accuracy of the concerned track point drops below certain threshold (and that's the case typically pretty often). The watch then, instead of interpolating the distance between last known good GPS coordinates, it uses either the internally calibrated stride length (when no HRM-Pro available), or the HRM-Pro calibration, in the exactly same way as it would do on a treadmill.

I wrote a Connect IQ app for troubleshooting the strange distance & pace discrepancies at good GPS tracks, and it was not too difficult to find the cause - Garmin watches (partially) use the indoor mode also during outdoor activities. 

trux said:

Calibrating the Treadmill manually is useless for the HRM-Pro use. You only need to calibrate it by GPS runs.

It turns out it is not good enough to use the automatic calibration for treadmill running. If you read my initial post, I got 1.6% error in distance using automatic GPS calibration, and then 8.5% and 13% using manual calibration.

"How big a deal are these percentages?" I was wondering...

I looked back at my 1mi. PB (I am not a fast runner), and I looked at my 2nd and 3rd best to put in perspective how hard it is to shave off a few seconds for me. The results are telling. An error in distance of 1.6% will turn my 6:55min/mi. into 7:01min/mi, which would be my 6th personal best.

The watch GPS is indeed accurate outdoors, but in this case, the use case is monitoring real-time pace. With GPS, there can be a lag or sudden variations in real-time pace and that is painful in hard intervals. Having an accurate way of knowing instant pace with HRM-pro is expected.

For indoors, the GPS calibration is not good enough, and the manual calibration doesn't work to do harder intervals on the treadmill. Maybe it is not a common use case, but it is mine.

Finally, since power is tightly correlated to pace, if pace is off, power if off.

In the end, Garmin provides for a manual calibration that fails to work so far.

I was hoping I could replace my Stryd with HRM-Pro, but it is not possible in the current situation.

As I wrote the manual calibration is useless if you use HRM-Pro. And when you use HRM-Pro, avoid the option "always" at the pace & distance parameter of the strap, use "indoors" only. It will assure the best accuracy - provided by GPS when GPS signal is optimal, and using the HRM-Pro estimation when the GPS signal is bad. And additionally, in this mode, the calibration continues to fine-tune with every your outdoor run, following so the evolution of your technique.

trux said:

As I wrote the manual calibration is useless if you use HRM-Pro

This is the issue. Manual calibration doesn't work.

I am OK with the accuracy outdoors. This is not the problem.