Ok - just how accurate is the Tanita? I'm in good health, have never been overweight and have exercised all my life. I would be considered muscular, 5'10" 178 and am in my 3rd year of riding. My waist is about a 33 and I'm 36. The Tanita scale today (I just did this for the first time) said my body fat was 17% !! I've got some rope and sharp instruments at the ready - HELP !