why standard form only in the range of 1 to 9?

Question

example:
B x 10^n where:
1<= B < 10
Why B only in this range?
My lecturer want me to find the reason why..
Please help me..
Thank you..

Answer 1

Convenience.

One can restrict things that far -- that's obvious, because you know how to do it.

But restricting them further would be very hard using the same notation for numbers we now have.