An Inventory item of the type "Package" allows a user to create an item which contains more than one item. For example a user can create a Glasses Package which has one all inclusive price or is priced per the parts which make it up.
The package must contain all of the elements needed for the package. Select the Add an Item to the Package button to add the various items that make up the package. For a set of glasses to be able to be created at invoice time you will need to add a frame and separately add two lens to the package. Having the inventory items separated in the package will allow the user to enter a prescription for each eye. If you enter a quantity of 2 for the lenses then only one prescription will be applied for both lenses. Having them separate allows for a different prescription in each lens.
The Pricing Rule field allows for the package to use the price set by the user for the complete package or have each item individual price used for determining the price of the package.
Packages are very powerful and we strongly recommend that you test your package before using it to insure that the price being applied is the one you expect.