There are two methods and both require a pair of related tables.
MainTable::cCode = States::Code
Where cCode is your calculation with the left function.
In States you have two fields, Code and State with values such as:
Now you can either place the States::State field directly on your Main Table layout or define a states field in your main table and use the looked up value auto-enter option to copy the value of States::State into MainTable::State.
Awesome. That was perfect. I was trying to script it or calculate it as in If...first number = 4, then "QLD" etc (it's disappointing that it didn't work that way) but I didn't think of it as a state "code" to lookup. Users will not need to modify that table (since no more states will probably made, at least in the lifetime of my database!) so it will work well.
Thanks for the prompt help.
If you do need to show related data that is subject to frequent updates, simply place the field from the related table on the layout instead of defining a looked up value. Then updates in the related table such as the states table we've discussed, will appear automatically.