The point of force to be assumed by the calculation of tooth form factor for spur and LACR gears is defined here. The drop down list allows the definition of force applied at tip or at the high point of single tooth contact (HPSTC). For low quality gears loading at the tip should be choosen because of the influence of pitch errors. For high quality gears the single contact point can be choosen to consider load sharing between several pairs of teeth. See AGMA 908-B89 Table 5-1 for limits of the load sharing.
For helical gears with an axial contact ratio mF εβ > 1 this input is not used.