40030
There are 210 4 digit combinations and 5040 different 4 digit codes.
Although the 4003 is kind of an improved 4001, still many bassists prefer the 4001, finally discontinued in the 80's. I guess it's personal preferences cause the 4003 is a great quality instrument.
120
There are 90 four-digit palindromes
4
4003
4003
24
-4
4
There are 840 4-digit combinations without repeating any digit in the combinations.