Harry Judge is measuring fluidity in a forceful way (8,5)

I believe the answer is:

pressure gauge

I'm a little stuck... Click here to teach me more about this clue!

'measuring fluidity in a forceful way' is the definition.
I can't tell whether this definition defines the answer.

'harry judge' is the wordplay.
'harry' becomes 'pressure' (I can't justify this - if you can you should give a lot more credence to this answer).
'judge' becomes 'gauge' ('gauge' can be a synonym of 'judge').
'pressure'+'gauge'='PRESSURE GAUGE'

'is' is the link.

Can you help me to learn more?

I've seen this clue in the Irish Times (Crosaire) and the Irish Times.

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