Error Message when calculting growth percentage

I was able to get the formula to work using the simplified notation calculator, but it was giving me the format error message.

Per my code below, I am trying to calculate ((V1+V2)/V1) -1. But it is not calculating anything. Please help!

var v1 = Number(this.getField("Original_Line_Amount)").valueAsString); 

var v2 = Number(this.getField("Overage_Amount").valueAsString); 

if (v2==0) event.value = ""; 

else event.value = (v1+v2/v1) - ; 

Thanks!