A follow-up....and because I respect you as the "just the facts, Sgt Joe Friday, no nonsense", then maybe you can make sense of this.

I found how someone is calculating this....again, for a bad sprint of 60 hours on an original guess of 33.5 hours, I figured the accuracy was 55.83%. But I've got a project manager saying it's about 21%. Here is how the PM is calcing it...this seems more like a factor than an accuracy percentage.

1 - abs ( amount estimated - remaining work left - time spent)
-----------------------------------------------------------------------------
amount estimated


so that....

1 -   abs (  33.5  - 0 - 60)
       ----------------------------
              33.5

1 -  ( 26.5)
      ----------  
        33.5

1 -  .791


accuracy:   21%