You can use the Microns reading on your machine and it will be more sensitive to accuracy than using the Mils reading..
This is because it takes 25.4 Microns to make 1 Mil, get it ? When you want to see if you removed just a little material from the spot, you will see the Microns number change immediately when you do..
The spot you showed 12 Mils is 304.8 microns - a LOT of material not necessarily all Paint in that area..
And yes, as has already been said, something happened there and was repaired and painted again..
The adjacent (?) area where you show just 2 mils is 50.8 Microns, a very low number and probably like that because someone rubbed the paint too long with a compound and probably the dirty, wool or wool blend 7" pad you see at most auto body paint shops..
It is all damaged there for lots of reasons, and cannot be helped that much at the low reading place, but perhaps my be able to come out better at the higher reading area..
What I always try to do on every car in the Shop is make the correction all "Match" as much as possible...
So, you should adjust your work on that damaged panel so as to not remove more material from the low area/s and see if you can match the correction if possible from the surrounding paint at that level only...
If the paint is good at the higher part of the panel especially along the Sight Lines - the area/s most eyes fall on when looking at the panel, then all that higher area can be corrected better and as your eyes go down the panel, the damaged areas can look about as good as they can get..
Just remember you cannot fix damaged by cracks or rock chips, etc., paintwork very much before you may start to make it worse..
Slower speeds for sure and watching very carefully what is going on, stopping frequently and wiping it off, measuring, etc..
Good luck !
Dan F
