Touchstone, benchmark (8)
I believe the answer is:
standard
I believe this clue is a double definition.
'touchstone' is the first definition.
(I know that touchstone can be written as standard)
'benchmark' is the second definition.
(I've seen this before)
(Other definitions for standard that I've seen before include "Reference point against which other things can be evaluated" , "Criterion, touchstone" , "sort of lamp" , "Established model - flag" , "Principle" .)