I have a table that has a string field "ANUM" that has values that always begin with 089. Then the 3 characters; 089, are followed by between 3 or 4 characters. So a typical value in this field might be 089213 or 0895146. There will never be more than 4 characters, which follows that the total number of characters will not exceed 7.

What I need is an expression that will "filter" out the 089 values, leaving the remainder behind. So the aforementioned values of 089213 and 0895146 would result, after the expression is run, in 213 and 5146, respectively.

str(strVariable) returns the number stored in intVariable as a string (so if intVariable = 0891234, str(intVariable = "0891234")
That value is then passed to the len() function which returns the strings length (len("0891234") = 7)
Then 3 is subtracted from it (7 - 3 = 4)
So what we now have is this:

Val(Right("0891234", 4))

which returns the first 4 characters in "0891234" counting from the right [starting form the 4 in other words] (this returns "1234")
Finally, val() turns "1234" back into a number 1234.

And Thanks for the both the Verbose AND the Condensed explanations!

Verbose Explination:

str(strVariable) returns the number stored in intVariable as a string (so if intVariable = 0891234, str(intVariable = "0891234")
That value is then passed to the len() function which returns the strings length (len("0891234") = 7)
Then 3 is subtracted from it (7 - 3 = 4)
So what we now have is this:

Val(Right("0891234", 4))

which returns the first 4 characters in "0891234" counting from the right [starting form the 4 in other words] (this returns "1234")
Finally, val() turns "1234" back into a number 1234.