Measure of distance unknown, a grade miscalculated (7)
I believe the answer is:
yardage
'measure of distance' is the definition.
'yardage' can be an answer for 'distance' (distance measured in yards). I am not certain of the 'measure of' bit.
'unknown a grade miscalculated' is the wordplay.
I cannot quite understand how this works, but
'unknown' could be 'y' (algebra) and 'y' is found in the answer.
'a' is present in the answer.
an anagram of 'grade' is 'rdage' which is located in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for yardage that I've seen before include "Distance gained (Am. football)" , "Quantity of fabric" , "Distance (eg in golf)" , "Distance in three-foot units" , "Golf or American Football statistic" .)