Setting up a custom fields for Customer Items will allow you to record a raft of different information. These are set up per Customer Item Type
From Admin \ Settings \ Customer Items \ Manage Customer Item Types - Edit Appliances
The Title is what will show in the Item Type screen. Data Type can be chosen from the drop down boxes, Decimals is activated when Number is chosen. The Product Field drop down box is for creating a link to the Product field for the Item.
40 Custom fields can be set up.