| mvp,
typically the issue of mismatch between the T6c and STrM is caused by not having the personal values set correctly and matching between the T6c and STrM.
Second possible cause is lose HR belt that causes large %error in HR recording - watch can not deal with this while STrM can fill in the gaps and that may cause huge difference.
Check the values in the watch and the STrM and see if they match. If so look at the error rate (you can do that in FB Athlete which is available for 30 days as free trial). It is likely one of those that cause the discrepancy. |