Watch App : HRV

I could possibly send you a dev version that outputs raw data. I would require you send me a copy of the raw data you have from the other device, so I can create a comparable output.

sure that sounds good. I also just sent in a support ticket to Wahoo, hopefully I'll get some meaningful reply.

Just to follow up my previous reply, i did further digging and found out that the Tickr X is just not sending out ANT+ RR data correctly. It's not the app's issue. weird.

Just to follow up my previous reply, i did further digging and found out that the Tickr X is just not sending out ANT+ RR data correctly. It's not the app's issue. weird.

Not so weird. My Garmin ANT+ HRM's occasionally send out bad RR data as well. But I had access to them while developing the app, so I have coded those problems out.

the Tickr X's ANT+ is not just occasionally bad, it's unusable. You can take a look at the screenshot below of its ANT+ & bluetooth output. It's weird in that the Tickr X is simultaneously sending out valid RR interval data through bluetooth while through ANT+ is not. So it's not an measurement issue but it just has something to do with its ANT+ implementation.

https://www.dropbox.com/s/dgikw273rrt4hl3/wahoo_tickrx_antPlus_issue.jpg

I use the HRV app with my Garmin Forerunner 920 XT and year-old heart rate monitor strap. I do a 3-minute timed HRV measurement every morning and I've noticed that, after the measurement, it usually says that the number of samples collected was lower than the number of samples expected, e.g. 120 samples vs. 144 expected.

Is this expected or does this indicate that I might have a problem with my HRM? Do most people experience these dropped samples across different watches and HRMs or should I be concerned that something is amiss?

In my experience there are a few different factors that I believe are likely to cause some drop-outs.
1/ Slouching when seated.
2/ Pressure taking some of the tension off the strap when prone.
3/ Occasional bad packet. Very few.
They are mostly caused by a bad connection, between either the skin, or the HRM contacts. If it's contacts, and a soft strap, you may find it takes more than 1 wash to bring it back to life. I recently soaked an unresponsive strap (that had already been washed) overnight in laundry soaker, then washed it again. It revived the strap.

At 120 of 144 over 3 minutes I wouldn't be too concerned, even though it's not ideal. Means you are effectively getting approx 2:30 min sample, which I believe will give an accurate result. I have taken dropped packets into account, and coded such that they should not negatively effect the final result.

There is one other possibility. One of the ways I detect a bad packet, is if it falls outside of a certain range. It is possible that a valid response might get ignored. However for it to be ignored it has to have a very high deviation, which would be highlighted by very high HRV results. I would expect a HRV result well in excess of 100 if it was happening regularly.

1/ doesn't apply as I am always lying down when I do the test.
2/ is possible; I will tighten the strap to see if it is better.
3/ could be possible as well. The HRM device is more than one year old but I recently replaced the soft strap, so it is basically new. I wonder if the older device could cause problems, though, and maybe I should get an entirely new HRM.
4/ My results are usually in the 70-90 range so it doesn't sound like the other possibility you described is the case.

This morning was 141 samples vs 141 expected, so clearly no problem today! I'll try tightening my strap to see if I can ensure a more consistent connection.

This morning I registered a 91, which is on the high side. I noticed that only 110 out of 141 expected samples were collected. So I ran a second 3-minute HRV test. This time 122 out of 141 expected samples were collected but the result was still very close: 90. So, based on this one small test, it seems that indeed dropped packets are not affecting the result too much. Good job! :)

Still, I wish I could figure out why one day I'm getting 141/141 and he next day only 110/141.