Step quantity allows you to have customers order in increments of minimums in a set number. e.g. if number set is 3 and you choose this, customer will have to order 3,6,9 etc.
To add a model number to your product go to the menu Products > View Products > You will now see all products available in your store.
To edit a product click on the "pencil icon" next to the product. Now click on the tab Specifics.
Scroll down to the section Step Quantity and add your products model number.
