Went up in a series of graduations to 500 (6)
I believe the answer is:
scaled
'went up' is the definition.
(scaling is a kind of going up)
'series of graduations to 500' is the wordplay.
I cannot really see how this works, but
'series' could be 'scale' (I have seen 'Series of notes' mean 'scale' so perhaps 'series' could also mean 'scale') and 'scale' is found in the answer.
'500' could be 'd' (Roman numeral for 500) and 'd' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'in a' acts as a link.
Can you help me to learn more?
(Other definitions for scaled that I've seen before include "Climbed; flaked off" , "Climbed - peeled off" , "Climbed or removed fish-flakes" , "Mounted" , "Got up" .)