The source code

    /**
     * @class Ext.ux.SliderTip
     * @extends Ext.Tip
     * Simple plugin for using an Ext.Tip with a slider to show the slider value
     */
    Ext.ux.SliderTip = Ext.extend(Ext.Tip, {
        minWidth: 10,
        offsets : [0, -10],
        init : function(slider){
            slider.on('dragstart', this.onSlide, this);
            slider.on('drag', this.onSlide, this);
            slider.on('dragend', this.hide, this);
            slider.on('destroy', this.destroy, this);
        },

        onSlide : function(slider){
            this.show();
            this.body.update(this.getText(slider));
            this.doAutoWidth();
            this.el.alignTo(slider.thumb, 'b-t?', this.offsets);
        },

        getText : function(slider){
            return String(slider.getValue());
        }
    });