The hardness depth is an input for material parameters. If it should be calculated by the software or if it is of no interest for through hardened bearings for example, then set this flag.
If the flag is not set, a check is made if the hardness depth is large enough.
Using the 
-button it can be defined if either the yield point or the fatigue limit is used to calculate the required hardness depth. The selection depends on the given load. If the calculation is done using a maximal load, the yield point can be used. If it is done using the equivalent load the fatigue strength is recommended. Also a required safety factor for the subsurface stresses against the yield point can be defined. It will be used for the calculation of the required hardness depth.
