Update pvl_spa.m

Author: DanRiley

pvl_spa.m

@@ -445,7 +445,9 @@
 end
 
 function [DeltaT]=calculate_deltaT(year, month)
-	
+% This function generates delta T based upon year and month using 
+% piecewise polynomial expressions.
+
     % The equations aren't meant to be used outside of the range of years
     % [-1999, 3000]
     if any(year < -1999 | year > 3000)
@@ -972,4 +974,4 @@
 0 0
 0 0];
 
-end
+end