I have the chain wear tool and that is how I checked the chain wear. In the last week twice when I was in the big ring and second largest on cassette when I got out the saddle my chain slipped off the large chain ring and went to the middle chain ring. I checked the front derailleur and it looked OK. This is when I thought I might as well replace the chain. When I got out the saddle and had the cassette in a smaller gear on the cassette I have not experienced such problems. Thanks for the input folks.