         resultLabel.text = readableString(solution)
         
         if resultLabel.text == NSLocalizedString("Number too large", comment: "Number being too large") {
-            previousValue = 0
+            previousValue = nil
         } else {
             saveToCoreData()
             previousValue = solution

    let divide = "÷"
    
    var results = [NSManagedObject]()
    var previousValue: Double
    var currentValue: Double?
    var currentOperator: String?
    var operationButtons: [CalculatorButton]?
    
    required init?(coder aDecoder: NSCoder) {
        previousValue = 0
        super.init(coder: aDecoder)
    }
    

    }
    
    @IBAction func onOperationTapped(sender: CalculatorButton) {
        if previousValue != nil {
            previousValue = Double(resultLabel.text!)!
            onEqualsTapped()
        }
        currentOperator = sender.titleLabel!.text!
        highlightOperationButton()
        previousValue = Double(resultLabel.text!)!
