Surface calculation (4)
I believe the answer is:
area
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">surface calculation</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for area that I've seen before include "land" , "field of study" , "Extent of a 2-dimensional surface" , "Expanse or neighbourhood" , "Succession, order" .)