A way of identifying weapon immediately (9)

I believe the answer is:

ataglance

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'a way of' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.

'weapon immediately' is the wordplay.
I cannot quite understand how this works, but
'weapon' could be 'lance' (lance is a kind of weapon) and 'lance' is located in the answer.
This may be the basis of the clue (or it may be nonsense).

'identifying' acts as a link.

Can you help me to learn more?

I've seen this clue in The Times.

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