- 1 milli-whatever is written as .001
- 1 micro .000001
- 1 nano .000000001
- 1 pico .000000000001
- 1 femto .000000000000001
Whenever you are making calculations, you want to use numbers as close to one as you can because inevitably you are going to encounter a multiply or divide by a zillion and if you started with a very big or very small number your result will be off the scale and your answer will be worthless.
Just for reference, a double precision number in today's common floating point format can have at most 16 significant digits,