Look for rounding of the tooth edges along with chips, brinling (looks like ripples) and contact pattern. Basically if it looks bad it probably is lol. If you google differential contact pattern you should be able to find pictures of what you are looking for for wear. The teeth should have sharp clean edges and not be rounded off. To get the ratio take the ring gear tooth count (EX 41) and divide by the pinion tooth count (EX 11), so 41/11 = 3.727272 or a 3.73 ratio
