Both my wife and I walk every morning the exact same walk. We walk on a track, so I know it is exactly a half a mile each time around. My watch only credits me .70 miles for two times around and hers credits her for a full mile. We walk for over an hour (usually doing about 3.5 miles total an hour) and she will get the full exercise heart rate time credit where mine only says I only exercised maybe 5 minutes. My watch will give me the same results when I am using the fitness app and when I am not. I have calibrated the watch many times. So I finally got around to taking it to the genius bar. They had me re-pair and reset it and set it up as new and a few other things. I was there for over 2 hours. We walked around the mall and tested it getting the same 30% less results. So they sent it into for repair. I bought another watch, mostly so I could test it to see what the results are. The first morning we walked it was perfect. It read that I was walking the full mile. The 2nd day it was giving me the exact same readings as my watch that was sent out for repair (.70 for every mile and almost no heart rate reading) I wear it snug and I know there was some problems with it reading heart rates with tattoos. I do not have any tattoos, so that is not the problem. Any suggestions are greatly appreciated.