Checking key measure of oxidisation (11)

'checking' is the definition.
The definition and answer can be both to do with social activities as well as being present participle verbs.
Maybe you can see a link between them that I can't see?

'key measure of oxidisation' is the wordplay.
I cannot really understand how this works, but
'key' could be 'g' (musical key) and 'g' is found within the answer.
'measure' could be 'in' (in is a kind of measure) and 'in' is located in the answer.
'oxidisation' could be 'rust' (rust is a kind of oxidisation) and 'rust' is found in the answer.
The remaining letters 'frat' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?