Tally, tie in with (9)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
correlate
(Other definitions for correlate that I've seen before include "To be linked to each other; trace role (anag.)" , "Establish a mutual relationship between (things)" , "Be complementary" , "Match" , "Bring (things) into correspondence" .)