Nominal shortages are usual (6)
I believe the answer is:
normal
'are usual' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for normal that I've seen before include "Ordinary, not extraordinary" , "Average or ordinary" , "Usual; at right angles" , "Conforming to a standard" , "Commonplace" .)