Number Representations

A real number r is represented internally as

r =  0.a1a2a3... * 10±xy

with mantissa  a1a2a3... and exponent xy.

r1=Sqrt[2];
r2=r1//N;

ScientificForm[r1] 
ScientificForm[1000.0*r1]
ScientificForm[0.00001*r1]

ScientificForm[{r2,1000.0*r2,0.00001*r2}]
(* mantissa and exponent of three numbers *)

r3=.22*10^-10//N;
r4=10^10//N;
Print["r3 + r4:  ",r3+r4]