Poorly designed gauges using millimetres might look a little foolish (4,4)
I believe the answer is:
mugs game
I'm afraid I can't even guess how this answer relates to the clue.
Can you help me to learn more?
(Other definitions for mugs game that I've seen before include "a worthless activity" , "Eggs a mum on to informal unprofitable activity" , "Foolish act" , "Charlie's activity?" , "Worthless enterprise" .)