Number changing is something I notice a lot too when not centered correctly or even comming from a differnt direction. This is why if it is repeatable I like to try to come at it from a differnt direction to see what numbers I can all get. I tell most around here that look at the numbers too much and tell me where there numbers read that are not the correct one, if it sound good work the coil around it and see what you get. Somewhere you will get the correct numbers. These 31 numbers i was getting were consistence the same with the tones in manual sensitivity, but were not as great of a signal in auto, but were fairly repeatable. I have dug good targets that dont sound as good as what these 31 sound, so this is why I feel if I get a lock on 31 it is a trash item, but if the numers are just jumping to 31 once in a while those I will check out more.
Rick