"How Does It Work? Tanita's patented "foot-pad" design sends a safe, low-level electrical signal through the body to determine its composition." From Tanita's website: http://www.bodytrends.com/store/product.asp?Product_Code=F2682&Cate...
Seems to be pretty accurate (sadly). It changes with diifferent hydration levels, so it's an encouragement to stay hydrated.