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.

Doesn't it have a dash indicator for when the pads are low - 40-50000 miles is about typical unless you are a lead boot.

When the pad lining itself is less than the backing plate the lining is riveted or glued to it's time for new pads. 2mm or less of lining it's time for brakes.

When that groove is virtually gone you need new pads. In theory, while you can still see the groove there's enough meat on the pads. I'd get it done now, then you don't need to worry for some time.