For understanding, there are lower limits of the weather, these are 0 and 100, for tires we set additional points.
The most important thing is the erroneous tire factor. At 0, we have a clear correspondence, the tires will change only when this level of precipitation is reached.
For example, Dry - 0, intermediate 22, rain 62.
If we set the factor equal to 30.
Dry 0+ (0-0) * 30/100 = 0 lower bound
Dry 0+ (22-0) * 30/100 = 6.6 which corresponds to 0.33 mm
In total, if the track dries, then dry tires will dress at 0.33 mm
Intermediate 22- (22-0) * 30/100 = 15.4 lower limit (0.77mm)
Intermediate 22+ (62-22) * 30/100 = 34 upper limit (1.7mm)
Intermediate will dress when the rain level drops by 1.7mm