The Harpenden Caliper has been the standard research caliper for many years. Virtually all the data, equations, tables, etc., relating skinfold thickness to % bodyfat in use today are based on studies done using the Harpenden. The Harpenden is also the most accurate skinfold caliper made, being within + or - 0.2 mm. and can be read to the nearest 0.1 mm. The Harpenden can measure up to 55 mm. Although this accuracy is far greater than is necessary for ordinary % bodyfat determinations. 1 year warranty.