TargetTalk

Im building a home range for air rifle 3 p for my son,found plans for frame from cmp but I cant find the height for target placement for standing,kneeling,prone,need help

5.5.4 Target Heights
Target holders on the range must facilitate the placement of the targets at the correct height.
Correct target heights, when measured from the level of the fi ring point to the center of the
target are:
 Prone position 0.5 meters (19.7 in.) (± 10 cm. or 4 in.)
 Standing position 1.4 meter (55 in.) (± 5 cm. or 2 in.)
 Kneeling position 0.8 meters (31.5 in.) (± 10 cm. or 4 in.)