   className: 'classifier'
   template: require '../views/classifier'
   marks: []
+  currentFrameIdx = 0 # keeps track of current (zero-indexed) frame
+
   events:
     'click button[name="play-frames"]'    : 'onClickPlay'
     'click button[name="invert"]'         : 'onClickInvert'
     'click button[name="finish-marking"]' : 'onClickFinishMarking'
     'click button[name="four-up"]'        : 'onClickFourUp'
     'click button[name="flicker"]'        : 'onClickFlicker'
+    'click button[name="next-frame"]'     : 'onClickNextFrame'
     # 'click input[name="current-frame"]'   : 'onClickRadioButton'
     'change input[name="current-frame"]'  : 'onChangeFrameSlider'
 

    # @markingSurfaceList.enable()

  activateFrame: (@active) ->
    @active = modulus +@active, @classification.subject.location.standard.length
    @showFrame(@active)


    # @setClassification @classification  # ...

    @invert = false

    @currentFrameIdx = 0

    window.classifier = @

