The Temple of Heaven in Beijing was built in 1420 against the Altar of Prayer Valley and has three floors. The diameter of the lower layer is 91 meters, the diameter of the middle layer is 80 meters, and the diameter of the upper layer is 68 meters. What percentage is the diameter of the upper layer less than the diameter of the lower layer?
北京天坛对祈谷坛建于1420年，共为三层．下层直径91米，中层直径80米，上层直径68米．上层直径比下层直径少几分之几？
<gadget id="calculator">91 - 68</gadget>
<output>23</output>

<gadget id="calculator">23 / 91</gadget>
<output>23/91 = around 0.252747</output>

<result>23/91 = around 0.252747</result>