code: function() {
  
      var
        plotOffset = this.plotOffset,
        position = this.lastMousePos,
        context = this.octx;
  
      if (position) {
        context.clearRect(
          Math.round(position.relX) + plotOffset.left,
          plotOffset.top,
          1,
          this.plotHeight + 1
        );
        context.clearRect(
          plotOffset.left,
          Math.round(position.relY) + plotOffset.top,
          this.plotWidth + 1,
          1
        );    
      }
    }
docs: Removes the selection box from the overlay canvas.