这是一张购货单,自动计算价钱的``
  麻烦给出个详细方向```function formatFloat(src, pos)
{
    return Math.round(src*Math.pow(10, pos))/Math.pow(10, pos);
}function update(){  var num1=Number(form1.count1.value);
  form1.sum1.value=num1*238;  var num2=Number(form1.count2.value);
  form1.sum2.value=num2*248;  var num3=Number(form1.count3.value);
  form1.sum3.value=num3*208;  var num4=Number(form1.count4.value);
  form1.sum4.value=num4*225;  var num5=Number(form1.count5.value);
  form1.sum5.value=num5*210;
  
  var num6=Number(form1.count6.value);
  form1.sum6.value=num6*16;
  
  var num7=Number(form1.count7.value);
  form1.sum7.value=num7*78;  var num8=Number(form1.count8.value);
  form1.sum8.value=num8*65;
  
  var num9=Number(form1.count9.value);
  form1.sum9.value=num9*120;function account10(){
  var num10=Number(form1.count10.value);
  form1.sum10.value=num10*198;
}
function account11(){
  var num11=Number(form1.count11.value);
  form1.sum11.value=num11*220;
}  var num12=Number(form1.count12.value);
  form1.sum12.value=num12*69;  var num13=Number(form1.count13.value);
  form1.sum13.value=num13*32;  var num14=Number(form1.count14.value);
  form1.sum14.value=num14*15;  var num15=Number(form1.count15.value);
  form1.sum15.value=num15*22;  var num16=Number(form1.count16.value);
  form1.sum16.value=num16*17.5;  var num17=Number(form1.count17.value);
  form1.sum17.value=num17*4.5;  var num18=Number(form1.count18.value);
  form1.sum18.value=num18*48;  var num19=Number(form1.count19.value);
  form1.sum19.value=num19*19;  var num20=Number(form1.count20.value);
  form1.sum20.value=num20*26;  var num21=Number(form1.count21.value);
  form1.sum21.value=num21*45;  var num22=Number(form1.count22.value);
  form1.sum22.value=num22*26;  var num23=Number(form1.count23.value);
  form1.sum23.value=num23*45;  var num24=Number(form1.count24.value);
  form1.sum24.value=num24*20;  var num25=Number(form1.count25.value);
  form1.sum25.value=num25*16;  var num26=Number(form1.count26.value);
  form1.sum26.value=num26*78;  var num27=Number(form1.count27.value);
  form1.sum27.value=num27*78;  var num28=Number(form1.count28.value);
  form1.sum28.value=num28*36;  var num29=Number(form1.count29.value);
  form1.sum29.value=num29*28;  var num30=Number(form1.count30.value);
  form1.sum30.value=num30*32;  var num31=Number(form1.count31.value);
  form1.sum31.value=num31*38;  var num32=Number(form1.count32.value);
  form1.sum32.value=num32*80;  var num33=Number(form1.count33.value);
  form1.sum33.value=num33*125;  var num34=Number(form1.count34.value);
  form1.sum34.value=num34*85;    var num35=Number(form1.count35.value);
  form1.sum35.value=num35*95;    var sum1=Number(form1.sum1.value);
  var sum2=Number(form1.sum2.value);
  var sum3=Number(form1.sum3.value);
  var sum4=Number(form1.sum4.value);
  var sum5=Number(form1.sum5.value);
  var sum6=Number(form1.sum6.value);
  var sum7=Number(form1.sum7.value);
  var sum8=Number(form1.sum8.value);
  var sum9=Number(form1.sum9.value);  
  var sum10=Number(form1.sum10.value);
  var sum11=Number(form1.sum11.value);  
  var sum12=Number(form1.sum12.value);
  var sum13=Number(form1.sum13.value);
  var sum14=Number(form1.sum14.value);
  var sum15=Number(form1.sum15.value);
  var sum16=Number(form1.sum16.value);
  var sum17=Number(form1.sum17.value);
  var sum18=Number(form1.sum18.value);
  var sum19=Number(form1.sum19.value);
  var sum20=Number(form1.sum20.value);
  var sum21=Number(form1.sum21.value);
  var sum22=Number(form1.sum22.value);
  var sum23=Number(form1.sum23.value);
  var sum24=Number(form1.sum24.value);
  var sum25=Number(form1.sum25.value);
  var sum26=Number(form1.sum26.value);
  var sum27=Number(form1.sum27.value);
  var sum28=Number(form1.sum28.value);
  var sum29=Number(form1.sum29.value);
  var sum30=Number(form1.sum30.value);
  var sum31=Number(form1.sum31.value);
  var sum32=Number(form1.sum32.value);
  var sum33=Number(form1.sum33.value);
  var sum34=Number(form1.sum34.value);
  var sum35=Number(form1.sum35.value);
  
  form1.sum36.value=formatFloat((sum1+sum2+sum3+sum4+sum5+sum6+sum7+sum8+sum9+sum12+sum13+sum14+sum15+sum16+sum17+sum18+sum19+sum20+sum21+sum22+sum23+sum24+sum25+sum26+sum27+sum28+sum29+sum30+sum31+sum32+sum33+sum34+sum35), 2);  var sum37=form1.sum36.value;
  form1.sum37.value=formatFloat((sum37*0.8),2);  
  
  var sum37=Number(form1.sum37.value);
  var sum38=Number(form1.sum38.value);
  form1.sum39.value=formatFloat((sum38-sum37),2);  
}