     // calculate payment on tap of calculate button
     @IBAction func calculateButtonAction(sender: AnyObject) {
         
+        // Set vars to grab string data from input, then convert to double.
         n = loanTerm
         p = (loanAmountTextField.text as! NSString).doubleValue
         i = (rateTextField.text as! NSString).doubleValue

        i = i/12
        print(i)
        
        let first = (1+i)**n
        let second = first * i
        let third = p * second

        
        print(fith)
        
        // display result to user
        resultLabel.text = "\(fith)"
        
    }
