function calcres(){
  var sz = resmag.TSize.value;
  var ln10 = Math.log(10);

  resmag.resarc.value = Math.floor(555/sz)/100.0;
  resmag.resmoon.value = Math.floor(555/sz*1.15)/100.0;
  resmag.starmag.value = Math.floor((Math.log(sz)/ln10*5+8.8)*10)/10.0;
  resmag.nakedeye.value = Math.floor((sz/.25)*(sz/.25)*10)/10.0;
}

function calcmag(){
  var sz = maxmag.TSize.value;

  maxmag.mm.value = Math.floor(sz*25.4);
  maxmag.mag.value = sz*50;
}

function getdisp(){
  var sz = imagsize.Tscope.value;

  if (sz == 2){
    imagsize.disp.src = "./jup_50.jpg"
  }
  else if(sz == 2.5){
    imagsize.disp.src = "./jup_60.jpg"
  }
  else if(sz == 3){
    imagsize.disp.src = "./jup_76.jpg"
  }
  else if(sz == 3.5){
    imagsize.disp.src = "./jup_90.jpg"
  }
  else if(sz == 4){
    imagsize.disp.src = "./jup_102.jpg"
  }
  else if(sz == 5){
    imagsize.disp.src = "./jup_127.jpg"
  }
  else if(sz == 6){
    imagsize.disp.src = "./jup_150.jpg"
  }
  else if(sz == 8){
    imagsize.disp.src = "./jup_200.jpg"
  }
  else if(sz == 12){
    imagsize.disp.src = "./jup_280.jpg"
  }
}