Each position in a decimal integer has a value that is a power of 10.

   n = 3   5   8  = 3*100 + 5*10 + 8*1
       |   |   |
      102 101 100
        
   

If a number has a decimal part, the positions to the right of the decimal are also powers of 10, but they are negative powers:

   n = 3   5   8  .  1   4  = = 3*100 + 5*10 + 8*1 + 1/10 + 4/100
       |   |   |     |   |
      102 101 100    10-1 10-2