It's CTAM in OCTAL!
The difference here is that we post using the octal, or base-8, counting system. This means that there are 8 numbers/symbols (in this case, 0-7) per unit, before progressing to the next. For example, the number 7 would also be 7 in octal, but 8 would be written as 10 in octal. Likewise, 15 in decimal is 17 in octal, but 16 (decimal) is 20 in octal.
Here's a link to the Wikipedia page, for more info about the octal number system: https://en.wikipedia.org/wiki/Octal
The same rules that apply to the other counting threads, also apply here.
Ready? We'll start:
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(In case you didn't know, there are various different number bases in use - the most common is decimal (base 10), which we use virtually all the time. The second most common is binary (base 2), which is used quite a lot in computing. Other common bases are base 8 (octal) and base 16 (hexadecimal).)
