No correlation between morning HRV apps

 I previously looked at Elite HRV and My Ithlete and found poor agreement between them.  I also tried HRV Logger and found even less correlation.  

This graph shows My Ithlete versus HRV Logger.  The graph of Elite HRV versus HRV Logger is similar.

All of this was using a Polar H7 chest strap with morning readings alternating between the different apps.  I believe HRV Logger is more accurate than the other apps, so I don't think this invalidates the results from HRV Logger.