The most logical measure is to use the level of the feet as recording zero, so that any measure that does not reach the toes is negative and any reach past the toes is positive (such as for PRT Sit and Reach for the Navy). However, using negative values is more difficult for statistical analyses, and for comparing results. The procedure for the Presidents Challenge version require that the box is made with 9 inches (23 cm) at the level of the feet, so reaching two inches past the toes is recorded as 11 inches. The Eurofit manual suggests having 15cm at the level of the feet, and also 10 inches has been used (NHL combine testing).