EXC_BAD_INSTRUCTION in Swift - xcode

Question

I'm brand new at Swift. So I did this tutorial to make a tip calculator and it worked fine. I started a new project to see if I could recreate it, keeping the original code as reference along the way. I created my app exactly the same way, but using different variable names.
I'm getting this error at the lblABVCalculated.text line:
Thread 1: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)
Any ideas why the following code wouldn't work?
Heading
import UIKit
class FirstViewController: UIViewController {
#IBOutlet weak var txtOG: UITextField!
#IBOutlet weak var txtFG: UITextField!
#IBOutlet weak var lblABVCalculated: UILabel!
var OG = ""
var FG = ""
var answer : Float = 0
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
#IBAction func btnCalculate(sender: UIButton) {
calculateABV()
}
#IBAction func btnClear(sender: UIButton) {
txtOG.text = ""
txtFG.text = ""
lblABVCalculated.text = "ABV"
}
func calculateABV() -> Bool {
OG = txtOG.text
FG = txtFG.text
var fOG = (OG as NSString).floatValue
var fFG = (FG as NSString).floatValue
answer = fOG * (fFG * 0.01)
var answerFormat : NSString = NSString(format: "%0.2f", answer)
lblABVCalculated.text = "ABV: \(answerFormat)"
// Thread 1: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)
return true
}
}