Starting at last, I am to rebuild hut for spherical coordinate measurement (7)
I believe the answer is:
azimuth
'spherical coordinate measurement' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'starting at last i am to rebuild hut' is the wordplay.
'starting at last' becomes 'az' (I can't explain this - if you can you should believe this answer much more).
'i am' becomes 'I'm' (contraction).
'to rebuild' indicates an anagram (I've seen this in other clues).
'hut' anagrammed gives 'uth'.
'az'+'im'+'uth'='AZIMUTH'
'for' acts as a link.
Can you help me to learn more?
(Other definitions for azimuth that I've seen before include "(In astronomy and navigation) angle of a bearing measured clockwise from North" , "Astronomical bearing" , "Horizontal angle of a compass bearing" , "Horiz. angle (of compass bearing)" , "Horizontal angle of a bearing clockwise from the north" .)