The probit model links the stress level to the failure probability through the chosen cumulative distribution function. The probit model can be expressed in terms of the shape and scale (Weibull distribution) or location and scale (all other distributions) of the chosen distribution.

The probability of unit failing at a given stress level can be restated as the probability that a unit's tolerance is less than a given stress level. The distribution of these probabilities is known as the tolerance distribution.

Parameter Estimates
Standard 95.0% Normal CI
Parameter Estimate Error Lower Upper
Mean 692.416 18.3649 656.421 728.410
StDev 111.612 19.4518 79.3167 157.058

For the windshield data using a normal distribution, Location = 692.416 and Scale = 111.612. The tolerance distribution models the probability that a particular windshield's breakage threshold is less than a given velocity.