Kaprekar numbers (Kaprekar routine)

Think of any number you like (3 or 4 digits are recommended). Rearrange the digits of that number to
create the largest possible number and the smallest possible number. Calculate the difference between them.
If you repeat this process, the result may eventually settle on a specific number.
(You can use any number up to 10 digits. What happens with a 5-digit number?)