Given that you showed us those error messages:

Argument "^\-933" isn't numeric in subtraction (-) at mycode.pl line 1
+15.
Argument "^\-1039" isn't numeric in subtraction (-) at mycode.pl line 
+115.
[download]

I'm wondering why you didn't show us the actual line 115 from the script that produced the error, along with the previous lines where values were assigned to the two variables involved (as well as the earlier line where a value is assigned to the variable that is being split).

Since the error message indicates that the values include initial caret and backslash characters ("^\"), my first guess would be that something odd is happening when assigning a value to the string that is being split on "," -- or something is altering the two values after the split -- involving regular expression operations.

Show us more of the actual code that caused the error -- in fact, see if you can construct a minimal self-contained script that includes the relevant value assignments, the split and the subtraction, and generates the error.

As others have pointed out, the "boiled down" information you've shown so far would not cause this error.