The Slim Guide Essential Kit includes: Slim Guide Skinfold Caliper, Dermografic Marker, and Calibration dowels to test calibration. THE SLIM GUIDE SKINFOLD CALIPER is the most widely used caliper in the world. It is the only low cost skinfold caliper accurate enough for professional use, with results comparable to the Harpenden caliper. Includes the book "How To Measure Percentage Bodyfat". Durable ABS construction. CALIBRATION DOWEL PIN SET Use this dowel set to certify calibration of your Harpenden, Skyndex, or Slim Guide skinfold caliper at 5mm and 16mm. Includes 2 pieces and instructions.