     @addCheckbox(fSkeleton, @user, "displayPreviewXZ", "Display XZ-Plane")
 
     fTrees = @gui.addFolder("Trees")
-    @activeTreeIdController = @addNumer(fTrees, @settings, "activeTreeID", 1, 1, "Active Tree ID")
+    @activeTreeIdController = @addNumber(fTrees, @settings, "activeTreeID",
+      1, 1, "Active Tree ID")
     if somaClickingAllowed
       @addCheckbox(fTrees, @settings, "newNodeNewTree", "Soma clicking mode")
     else

    @addFunction(fTrees, @settings, "deleteActiveTree", "Delete Active Tree")

    fNodes = @gui.addFolder("Nodes")
    @activeNodeIdController = @addNumer(fNodes, @settings, "activeNodeID", 1, 1, "Active Node ID")
    @commentController =
    (fNodes.add @settings, "comment")
                          .name("Comment")

                          .onChange((v) => @set(propertyName, v,  Boolean))

  addSlider : (folder, object, propertyName, start, end, step, displayName, onChange) =>
    unless onChange?
      onChange = (v) => @set(propertyName, v, Number)
    return (folder.add object, propertyName, start, end)
                          .step(step)
                          .name(displayName)
                          .onChange(onChange)

  addFunction : (folder, object, propertyName, displayName) =>
    return (folder.add object, propertyName)
                          .name(displayName)

  addNumber : (folder, object, propertyName, min, step, displayName) =>
    return (folder.add object, propertyName)
                          .min(min)
                          .step(step)
