How to read the wear indicator groove in disc brake pad, Civic?

The groove is now about 1 millimeter deep, so I'm thinking it is time to have my mechanic replace them soon. But I don't know how deep they were to begin with. Not sure if I should keep using these for a while or not. Can anyone tell me the original depth of the groove or whether I should wait or act now?

2006 Honda Civic LX sedan, front wheels.

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