/* carFuel.js -- metric|US|Imperial fuel ratings - 2007 11 28
   access is thru the form element id 'fuel'
   l,k are inputs for litres and kilometres
   m,g are inputs for miles and gallons U.S.
   mi,gi are inputs for miles and gallons Imperial
   d is display area for suitable messages
   created by john russell, ve3ll@rac.ca */
/* validated with JSlint 2007 11 28 */
cf=0.264/0.621; // l/k --> g/m conversion factor
ui=160/128; // U.S. to Imperial gallon factor

function roundoff(x,y){
   scale=Math.pow(10,y);return Math.round(x * scale)/scale;}

function fromMetric(){ // thru U.S.
   l=document.getElementById('l').value;
   k=document.getElementById('k').value;
   rat=l/k*cf; rat=1/rat; // must invert for u.s. way!
   document.getElementById('m').value=roundoff(rat,2);
   document.getElementById('g').value="1";
   rat=rat*ui; // now make it imperial volume
   document.getElementById('mi').value=roundoff(rat,2);
   document.getElementById('gi').value="1";}

function fromUS(){
   m=document.getElementById('m').value;
   g=document.getElementById('g').value;
   rat=m/g*ui; // to Imperial
   document.getElementById('mi').value=roundoff(rat,2);
   document.getElementById('gi').value="1";
   rat=g/m; rat=rat/cf*100; // must invert!
   document.getElementById('l').value=roundoff(rat,2);
   document.getElementById('k').value="100";}

function fromIMP(){
   m=document.getElementById('mi').value;
   g=document.getElementById('gi').value;
   rat=m/g/ui; // to US measure
   document.getElementById('m').value=roundoff(rat,2);
   document.getElementById('g').value="1";
   rat=g/m; rat=rat/cf*100*ui; // must invert!
   document.getElementById('l').value=roundoff(rat,2);
   document.getElementById('k').value="100";}

function clrForm() {
document.getElementById('l').value=" ";
document.getElementById('k').value="100";
document.getElementById('m').value=" ";
document.getElementById('g').value="1";
document.getElementById('mi').value=" ";
document.getElementById('gi').value="1";
document.getElementById('d').value="Comments...";
document.getElementById('l').focus();}

function about() {
alert('Fuel Calculator version 2.0 by John W.M. Russell.\n'+
      'written 2007 06 02; revised 2007 11 28\n' +
      'Feel free to copy carfuel.js for your own use.');
document.getElementById('l').focus();}