Using the Park 3.2 tool always for me showed that my chain was worn out, where as the Pedro ChainChecker Plus2 showed it was OK. I decided to wait until the Pedro tool showed a worn out chain and I believe this also allowed for the cassette to wear out earlier. So, I came to the conclusion that a chain is cheaper than a cassette and just replace the chain when the Park tool tells me. I know the chain still has some life left, but it is not worth it to me to try and get more 'miles' out of the chain. I believe your gravel trail riding is a factor. It is like sandpaper...