Formula for Intensity
 vs. m:
 
 
 With mathematics which we won’t derive
 here, you can show this is equivalent to the equation:
 
  
 This
 second equation is easy to use on a calculator.
  
  If you remember that log( 10n )  =  n, for
 example 
  log( 104) = 4,   
 log (105) = 5,   
 log(106) = 6, 
  you can use it even without a calculator.