A vertical ascent is, truly (8,2)
I believe the answer is:
straight up
This clue might be a double definition.
'a vertical' is the first definition.
(I've seen this before)
'is truly' is the second definition.
(I've seen this before)
'ascent' acts as a link.
I am not very happy about this link. It may belong to one of the definitions.
Can you help me to learn more?
(Other definitions for straight up that I've seen before include "truly" , "taking shortest route?" , "Exactly how one reaches summit" , "On the level" , "It's the quickest way to get high" .)