See>>> http://www.cloudtag.com/

And it’s been ‘validated’!!! >>> http://www.cloudtag.com/2015/10/26/accuracy-results-from-user-testing/

Sorry – correlation is just not the way to validate 2 methods!

They should specify an acceptable margin for the paired differences (2 measures are never identical)

The British Standard is – 95% of all measurements should be with 2SD of the mean difference

 

Then they should measure the differences they get

That way they quantify the precision of the difference as well by putting confidence limits on it

 

Mind you no-one ever knows how to do it properly (statistically)!