Kureishima said:
I just don't see how infinite 9 equal auto-up, how infinite 8 doesn't equal auto-up and so forth.
It's a special property of 'Base (whatever)'.
Base 10 (what we use) contains the following numbers: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9. After "9" you move into the tens column and start again. In the Base 10 number system, any infinite recurring trail of 9s is equal to the number which looks 'above it' (i.e. 0.99... = 1, 2.499... = 2.5)
Base 4 contains the following numbers: 0, 1, 2, 3. After "3" you move into what we would call the tens column. So the first ten numbers in Base 4 are: 1, 2, 3, 10 [4], 11 [5], 12 [6], 13 [7], 20 [8], 21 [9], 22 [10] (base 10 equivalent in square brackets). For the Base 4 system, any recurring trail of 9s is equal to the number which looks 'above it'. (i.e. 0.33... = 1, 13.333... = 20)
Hexadecimal is a Base 16 system used in computing containing the following numbers: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F. I won't go through the details of how hex works (it's the same principle as the others), but in hex a number of 0.FFF... = 1, 2.5FFF... = 2.6, 9.FFF = A.
Basically, this rule applies whenever you have a recurring trail of the highest possible unit in any base system.