but not for clocks. with BCD less calculation is required as you can increment individual segments at a time (e.g you dont want to have to retotal the whole time every second - that would require extra cpu cycles)
The next number to the left is double the previous number. So the pattern goes like this:
0 - 0 - 0 - 0 - 0 - 0 - 0
64 32 16 -8 - 4 - 2 - 1
and so on from 64 -> 128 -> 256 etc.
Remember the number to the left is double the previous one.