function yurtcalc() {
   // -- yurt calculator, written by Rene K. Mueller
   //    for http://Housing.byRene.com
   //    inspired by the dome calculator at DesertDomes.com
   // history:
   // 2006-10-29: added piewise canvas calculation
   // 2006-01-08: volume added
   // 2005-09-29: htot corrected
   // 2005-09-27: misc corrections
   // 2005-08-09: first version
   
   var f = document.calc;
   var h; var d;

   h = f.h.value*Math.tan(f.akhana.value/2/180*3.141);
   f.lkhana.value = format(Math.sqrt(f.h.value*f.h.value+h*h));
   f.w.value = format(f.d.value*3.141/f.npoles.value);
   f.wkhanaholes.value = format(f.w.value/(Math.sin(f.akhana.value/180*3.141/2)*2));
   f.nkhanaholes.value = Math.floor((f.lkhana.value-12)/f.wkhanaholes.value+1);
   f.c.value = format(f.d.value*3.141/100);
   f.apoles.value = format(360/f.npoles.value);
   f.Awall.value = format((f.d.value/100.0)*3.141*(f.h.value/100.0));
   f.Awalld.value = f.c.value+" x "+format(f.h.value/100);
   if(f.calctype[0].checked) {
      f.aroof.value = format(Math.atan((f.htot.value-f.h.value)/(f.d.value/2-f.dwheel.value/2))/3.141*180);
   } else {
      f.htot.value = format(f.h.value*1+(Math.tan(f.aroof.value/180.0*3.141)*(f.d.value/2-f.dwheel.value/2)));
   }
   f.Vtotal.value = format(
      ((f.htot.value-f.h.value)*(f.d.value/2)*(f.d.value/2)*3.141/3 + 
      (f.d.value/2)*(f.d.value/2)*3.141*f.h.value)/(100*100*100));
   f.khanaleft.value = Math.round(f.lkhana.value-(f.nkhanaholes.value-1)*f.wkhanaholes.value); 
   f.nkhanasections.value = Math.floor(f.c.value/f.lkhanasection.value)+1;
   f.nlaths.value = f.npoles.value*2.0+f.nkhanaholes.value*2/2+f.nkhanasections.value*2;
   
   d = f.d.value/2-f.dwheel.value/2;
   h = Math.tan(f.aroof.value/180*3.141)*d;
   //f.lpole.value = format(Math.pow(h*h+d*d,0.5));
   f.lpole.value = format(Math.sqrt(h*h+d*d));
   d = f.d.value/2;
   h = Math.tan(f.aroof.value/180*3.141)*d;
   //f.lroof.value = format(Math.pow(h*h+d*d,0.5));
   f.lroof.value = format(Math.sqrt(h*h+d*d));
   
   f.droof.value = f.lroof.value*2;
   
   f.Afloor.value = format((f.d.value/2/100)*(f.d.value/2/100)*3.141);
   f.Aroof.value = format(((f.lroof.value/100.0))*((f.lroof.value/100.0))*3.141);
   f.Aroofd.value = format(f.lroof.value*2/100)+" x "+format(f.lroof.value*2/100);
   f.Arooflo.value = format((f.lroof.value/100*2)*(f.lroof.value/100*2)-f.Aroof.value);
   f.wwheel.value = format(f.dwheel.value*3.141/f.npoles.value);
   f.acutoff.value = format((f.lroof.value*2*3.141-f.d.value*3.141)/(f.lroof.value*2*3.141)*360);
   f.wcutoff.value = format(Math.sin(f.acutoff.value/2/180*3.141)*f.lroof.value*2);
   var l; var lw = f.wlane.value; var off = 0; var tot = 0; var out = "";
   var dr = f.droof.value*1+f.wroofx.value*2;
   for(l=1; (l+off)*lw<dr; l++) {
      var w = 0;
      if(l*lw>=dr/2) {
         if(off==0) {
            w = format(dr/100);
         }
         off = -1;
      }
      if(w==0) {
         var b = dr/2-(l+off)*lw;
         w = Math.sqrt((dr/2)*(dr/2)-b*b)*2;
         w = format(w/100);
      }
      tot += w;
      if(l>1) out += "\n";
      out = out+"Lane #"+l+" = "+w+" x "+format(lw/100)+" m";
   }
   f.laneslo.value = w+" x "+format(((l+off)*lw-dr)/100);
   f.llanestot.value = format(tot)+" x "+format(lw/100);
   f.lanes.value = out;

   f.co.value = format(f.d.value*3.141/f.npie.value);
   f.ci.value = format(f.dwheel.value*3.141/f.npie.value);
   f.pl.value = f.lpole.value;
   
   if(f.h.value*1<=lw) {
      f.totalcanvas.value = format(tot+f.c.value*1)+" x "+format(lw/100);
      f.wallnote.value = "one lane";
   } else {
      f.totalcanvas.value = format(tot+(Math.floor(f.c.value*100/lw+1)*f.h.value)/100)+" x "+format(lw/100);
      f.wallnote.value = Math.floor(f.c.value*100/lw+1)+" lanes";
   }
   f.costcanvas.value = format((tot+f.c.value*1)*f.costpercanvasm.value);
   f.costkhana.value = format(f.nlaths.value*f.costperkhana.value)
   f.costpoles.value = format(f.npoles.value*f.costperpole.value);
   f.totalcost.value = format(f.costcanvas.value*1+f.costkhana.value*1+f.costpoles.value*1);
   return;
}

function format(a) {
   return Math.round(a*100)/100;
}