Thanks!
I actually did not really pay to much attention to the math and just used that version based on performance.
(the other version of the code written by 'scjurgen' all use floating point math)
The 16 bits in an Arduino short seemed reasonable, considering the 10 bit ADC.
(16 vs 8 bits for the short type: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1261049420/1#1)