How to (Worm Gears)

How to change and select the values from the Assembly Dimensions area?

The values of the center distance, Z1, Z2 and the other fields from Assembly Dimensions area are coming from the database and these values are standard-based. As per the input given to options Tooth Diametral Quotients or Transmission Ratio in the Gearing Parameters area, these fields are updated accordingly. User is allowed to select any of the given combinations for designing the worm gear.