A scale showing quantity (6)
I believe the answer is:
amount
I believe this clue is a double definition.
'a scale' is the first definition.
(thesaurus)
'quantity' is the second definition.
(synonyms)
'showing' acts as a link.
(Other definitions for amount that I've seen before include "Add up or be equivalent to" , "Quantity, sum" , "A quantity or total of anything" , "value" , "Sum of money" .)