Script to subtract decimals

I am trying to subtract 3 fields that will all be decimals. I had the format changed to numbers and 2 decimals under format but in the script I have:

v1=this.getField("text17").value;
v2=this.getField("text18").value;
v3=this.getField("text19").value;

event.value = v1-v2-v3

It was working before I changed the format to decimals, just curious what I need to add to make it now work with decimals. I'm sure it's a simple solution I'm just not sure what to put in there to fix it. Any help is appreciated!