When defining abbreviations that are not common to the user population, a simple rule should be used that users understand and recognize.
Additional Information:
Abbreviation by truncation is the best method, except when word endings convey important information. When a truncation rule is used, abbreviations are easy to derive and easy for a user to decode. If an abbreviation deviates from the consistent rule, it may be helpful to give it some special mark whenever it is displayed.