Prior to use I read the instructions, watched the videos because of the coat I didn't wan to screw it up. Well, I screwed it up because it doesn't say that you can sweat too much until you did and read the FAQ as to why. At 45 minutes the patch was "full" at 75 minutes it couldn't be read. My workout consisted of VO2 max intervals with a lot of rest so not even a really tough session. Now I know to stop before it's full and to scan the patch. That doesn't seem like it's a true picture of sweat rate and electrolyte loss when I can' teven finish the workout. I will recommend to friends with the above warning because it seems like it worked for others.