error Thread 1 signal SIGABRT

i'm following a course in a youtube for swift and i did every thing same but i'm facing Thread 1: signal SIGABRT

Here is the code

i'm trying to create a Calculator and i only create the digits and the result display

ViewController

import UIKit

 class ViewController: UIViewController
  {
      @IBOutlet weak var ResultDisply: UILabel!



@IBAction func AppendDigit(sender: AnyObject) {
    let Digit = sender.currentTitle
    print("Digit = (Digit)")

} 
 }

Error:

016-06-18 22:22:19.783 Calculator[26381:914616] -[Calculator.ViewController  aDigit:]: unrecognized selector sent to instance 0x7fb580daaa70
       2016-06-18 22:22:19.823 Calculator[26381:914616] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-      [Calculator.ViewController aDigit:]: unrecognized selector sent to instance   0x7fb580daaa70'
*** First throw call stack:
   (
0   CoreFoundation                      0x0000000102c00d85 __exceptionPreprocess + 165
1   libobjc.A.dylib                     0x00000001049a4deb objc_exception_throw + 48
2   CoreFoundation                      0x0000000102c09d3d -[NSObject(NSObject) doesNotRecognizeSelector:] + 205
3   CoreFoundation                      0x0000000102b4fcfa ___forwarding___ + 970
4   CoreFoundation                      0x0000000102b4f8a8 _CF_forwarding_prep_0 + 120
5   UIKit                               0x000000010342aa8d -[UIApplication sendAction:to:from:forEvent:] + 92
6   UIKit                               0x000000010359de67 -[UIControl sendAction:to:forEvent:] + 67
7   UIKit                               0x000000010359e143 -[UIControl _sendActionsForEvents:withEvent:] + 327
8   UIKit                               0x000000010359d263 -[UIControl touchesEnded:withEvent:] + 601
9   UIKit                               0x000000010349d99f -[UIWindow _sendTouchesForEvent:] + 835
10  UIKit                               0x000000010349e6d4 -[UIWindow sendEvent:] + 865
11  UIKit                               0x0000000103449dc6 -[UIApplication sendEvent:] + 263
12  UIKit                               0x0000000103423553 _UIApplicationHandleEventQueue + 6660
13  CoreFoundation                      0x0000000102b26301 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
14  CoreFoundation                      0x0000000102b1c22c __CFRunLoopDoSources0 + 556
15  CoreFoundation                      0x0000000102b1b6e3 __CFRunLoopRun + 867
16  CoreFoundation                      0x0000000102b1b0f8 CFRunLoopRunSpecific + 488
17  GraphicsServices                    0x0000000107296ad2 GSEventRunModal + 161
18  UIKit                               0x0000000103428f09 UIApplicationMain + 171
19  Calculator                          0x0000000102a1c4f2 main + 114
20  libdyld.dylib                       0x000000010546892d start + 1
21  ???                                 0x0000000000000001 0x0 + 1
)
  libc++abi.dylib: terminating with uncaught exception of type NSException
 (lldb)