Error allowance (6)
I believe the answer is:
margin
'error allowance' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for margin that I've seen before include "Blank space that surrounds the text on a page" , "Bound" , "Edge; room for error" , "Blank space around the edge" , "Permissible difference" .)