         }
     }
     
-    //Description of history
-    fileprivate var descriptionAccumulator = ""
-    
+    // MARK: Description
     //Description of sequence of operands/operations that lead to the result
     var description : String {
         get{


//Model class (Business Logic for Calculator)
public class CalculatorBrain {
    
    //accumulate result of calculator
    fileprivate var accumulator = 0.0
    fileprivate var decimalDigits: Int
    //internal program of property list items (Double if operand, String if operation)
    fileprivate var internalProgram = [AnyObject]()
    
    init(decimalDigits: Int) {
        self.decimalDigits = decimalDigits

        }
    }
    
    // MARK: Operations
    //Used by View Controller to reset accumulator to be operand
    func setOperand(_ operand: Double){
        internalProgram.append(operand as AnyObject)
