What is the meaning of the phrase "moving the needle"?

I believe this is a reference to the old analog Vu meter used in audio recording. Vu stood for Volume Units. When recording, some audio sources were not even loud enough to make the needle move off the bottom- in other words it was too faint to be of much use to record.

So saying that something is moving the needle means that it is enough to register or make a difference to the user- enough for the user to take note of

Make a significant difference. This would be referring to the needle of a measurement instrument; moving the needle would be really showing up on the measurement scale.

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