Let's re-write 10^(-3)
it is actually = 1 x 10^(-3)
Moving the decimal point to the left three place on the 1 (because the power is -3)
we get .001 - just like Google calculator
So, 10^(-3) kg = 1 x 10^(-3) kg or .001 kg or 1 g
and
10^(-3)kg = 1 x 10^(-3)kg = .001 kg = 1 grams
kg = Kilograms or three places to the right of the decimal point.