Now the unit was sent back for repair, and I need to continue my workout with the Polar FT4. As all the training for sub 4 was completed, I only planned easy runs for these few weeks just to maintain the momentum. Most of the workout will be running at easy pace with <140BPM. Still some adjustment needed to run solely by effort, but I think soon I will get used to it. Hopefully 910XT will return home timely for the APBIM.