The Accu-Measure Skinfold Caliper is an accurate, durable, reliable, and easy-to-use tool for measuring body fat. It is recommended in Body-for-LIFE and endorsed by the World Natural Bodybuilding Federation. Accu-Measure Personal Body Fat Testers have gold standard accuracy to within 1.1 percent of underwater weighing results! A clinical study published in the Journal of Strength & Conditioning Research by the National Strength & Conditioning Association sited the following key findings:Self-testing of percent body fat with the Accu-Measure was as accurate as results from multi-site measurements and calculations taken by an experienced clinical investigator using a Lange caliper. Percent body fat calculations with the Accu-Measure were within 1.1 percentage points of underwater weighing results. This kit also includes the how to measure your % bodyfat book.