(1+(1/2)+(1/3)+...+(1/1999))*((1/2)+(1/3)+...+(1/2000))-(1+( 1/2)+(1/3)+...+(1/2000))*((1/2)+(1/3)+...+(1/1999)).
(1+(1/2)+(1/3)+…+(1/1999))*((1/2)+(1/3)+…+(1/2000))-(1+(1/2)+(1/3)+…+(1/2000))*((1/2)+(1/3)+…+(1/1999))．
<gadget id="calculator">1 / 2_000</gadget>
<output>1/2_000 = around 0.0005</output>

<result>1/2_000 = around 0.0005</result>