Moving a decimal point one place to the left amounts to dividing by 10, e.g. 13.9 is the same
as
139
10
. (Similarly, moving the point to the right is the same as multiplying by 10.)
Moving it again to the left means dividing by 10 again. So, having moved the point 2 places
to the left amounts to dividing by 100. Moving it 3 places to the left amounts to dividing by
1000, and so on.