Bore Gauge Help

Thanks, its a 383. I haven't removed the ridge, just cleaned the crap off it. The ridge doesnt appear very deep. The std bore is 4.25 for a 383 and the ridge is measuring 4.26 so I'm guessing this has had 10 tho bore in the past or my gauge needs calibrating....

What sort of measurements am I looking for down the hole, and how far?