Please scan definitions before meeting : Update Requirements for Github issue #188

In the hope of wrapping up the discussion of Github issue #188 today, I 
have assembled the history of this issue into one document so we had 
links to the meeting discussions and the evolution of this Requirement 
over recent months.  You can skip over the history if you are not 
interested.

Thank you to Sarah for the proposal to wrap up the issues brought up in 
the meeting of the 19th. I have included Sarah's proposal and have taken 
the time to look up the definitions of the different terms that she 
proposed as options in the hope of saving time.  They are at the end of 
the document.

History - Github Issue #188 - Multiple Ways to Measure 
<https://docs.google.com/document/d/17lkBBpSYchGcr-2KB8Ud7-7RTfziAo_TlxMT7WpYCno/>

Please take a few minutes before the meeting to scan the definitions so 
we can vote on changes today.