Whilst investigating Zepp's heart-rate data, I found that the app seems to use the values 255 and 254 as special values (indicating missed/skipped reads).
Looking at the heart-rate data that we've pulled out of the Gadgetbridge database:

It looks like it's the watch itself supplying these values.
The result is that we're currently writing quite a few 255's into Influx.
The values can easily be excluded at querytime, but in zepp_to_influxdb I decided to skip these values so it'd probably make sense to keep things consistent by doing the same here.
Activity
26-Aug-23 09:49
assigned to @btasker
26-Aug-23 09:50
mentioned in issue jira-projects/MISC#34
26-Aug-23 09:56
mentioned in commit 30a73d4156f0a60766a735e0c48a21d076412aec
Commit: 30a73d4156f0a60766a735e0c48a21d076412aec Author: B Tasker Date: 2023-08-26T10:54:32.000+01:00Message
Filter special values out of heart rate data (utilities/gadgetbridge_to_influxdb#1)
The Bip uses 255 and 254 as special values - as a result, they appear quite regularly. Outside of life-threatening events, these values shouldn't occur.
This change checks the value of any field called
heart_rate, so will catch activity data as well as through-the-day monitoring30-Jan-24 10:28
mentioned in commit 852ccef7f81d49caa01ccd0514d656f5c9a6ba93
Commit: 852ccef7f81d49caa01ccd0514d656f5c9a6ba93 Author: B Tasker Date: 2024-01-30T10:28:23.000+00:00Message
fix: Env variable name is wrong in README #1