var unit_=1;
var unit_dg=1;
var unit_km=110.8910224;
var unit_m=110891.0224;
var unit_cm=11089102.24;
var unit_mm=110891022.4;
var unit_nmi=59.88;
var unit_mi=68.90;
var unit_yd=121271.63;
var unit_ft=363814.89;
var unit_in=4365778.73;

function toUnits(aVal,unitA,unitB) {
  return eval('aVal/unit_'+unitA+'*unit_'+unitB);
}

function setUnits(obj) {
  sunits=obj.options[obj.selectedIndex].value;
  v_scale=document.fMain.hScale.value;
  v_grid=document.fMain.tGrid.value;
  document.fMain.tScale.value=toUnits(v_scale,cunits,sunits)*v_grid;
}

function setScale() {
  v_scale=document.fMain.tScale.value;
  if(v_scale>0) {
    sunits=document.fMain.sUnits.options[document.fMain.sUnits.selectedIndex].value;
    v_grid=document.fMain.tGrid.value;
    document.fMain.hScale.value=toUnits(v_scale/v_grid,sunits,cunits);
  }
}