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

            return nil
        }
        
        switch solutionOperator {
        case plus:
            return previousValue + secondValue
        case minus:
            return previousValue - secondValue
        case multiply:
            return previousValue * secondValue
        case divide:
            return previousValue / secondValue
        default:
            return nil
        }

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