Custom Calculation Script in Adobe Acrobat Pro DC

I already have a custom calculation script setup but I wanted to fix it a bit.

var v1 = Number(this.getField("NMS").value); 

var v2 = Number(this.getField("CMS").value); 

var v3 = Number(this.getField("CMS").value); 

if (v3==0) event.value = ""; 

else event.value = (v1-v2)/v3;

The script is giving me what I want in percentage. But what if I enter $5,000 in field "CMS" but left a $0.00 or blank in the field "NMS" yes it will give me a -100% in percent box but that's not what I want. I want the percentage to stay as "0.00" because if I do it the other way around such as $5,000 in the field of "NMS" but left a a $0.00 or blank in the field I get a "0.00" in percentage box.

I need help from anyone.