There are 3 different kinds of tanning packages, Minutes, Sessions, and Memberships. Although you don't need to sell a customer a tanning package, it is the usual way of doing business at tanning salons. This keeps the customer coming back for more tans, and offers a convenience to the customer of only having to pay once in a while.
Each different tanning package must also have an Item Type, and each item type is of a certain Inventory or Pack Type. There are 3 Pack Types for tans: Minutes (T), Sessions (U), and Memberships (W). These are chosen when you setup the Item Type.
We have setup 4 item types here. Notice that both the Monthly (MP) and the Tan Membership (UN) are Membership Pack types. This means that Tanning Packages that have these Item Types selected will follow the rules for a membership.
However, you really only need Pack Types for the kind of packages you sell. If you don't sell minute packages, you won't have occasion to setup a minute pack type.
Everything will be obvious when you actually add a Tanning Package.