if this were a code review i'd point out the following:

• use strict; and -w
• your formatting is inconsistent. eg, the line:

  $VX = ($SX2*$Xn - $Sx * $Sx)/($Xn*$Xn);

• i'd suggest using a HEREDOC to print the output instead of 27 or so print statements.

otherwise, the code is pretty straightforward, the variables are generally well-named, and the math looks right to me. so a ++ despite my nitpicks.

anders pearson