function calculatetime(form) {
	//  get conversion factors from selected options
	var i = form.distunits.selectedIndex;
	var distunitsvalue = form.distunits.options[i].value; 
	var j = form.speedunits.selectedIndex;
	var speedunitsvalue = form.speedunits.options[j].value;
	//  calculate time in seconds    
	form.secondvalue.value = (form.distvalue.value * distunitsvalue) / (form.speedvalue.value * speedunitsvalue);
	//  convert to hours, minutes, seconds    
	form.hourvalue.value = parseInt(form.secondvalue.value / 3600);
	form.secondvalue.value = form.secondvalue.value - (form.hourvalue.value * 3600);
	form.minutevalue.value = parseInt(form.secondvalue.value / 60);
	form.secondvalue.value = parseInt(form.secondvalue.value - (form.minutevalue.value * 60));
	return true;
}
function calculatedistance(form) {
	//  get conversion factors from selected options
	var i = form.distunits.selectedIndex;
	var distunitsvalue = form.distunits.options[i].value; 
	var j = form.speedunits.selectedIndex;
	var speedunitsvalue = form.speedunits.options[j].value;
	//  convert time to seconds
	var temp = ((parseFloat(form.hourvalue.value) * 3600) + (parseFloat(form.minutevalue.value) * 60) + parseFloat(form.secondvalue.value));
	//  calculated distance
	form.distvalue.value = ((form.speedvalue.value * speedunitsvalue) * temp) / distunitsvalue; 
	return true;
}
function calculatespeed(form) {
	//  get conversion factors from selected options
	var i = form.distunits.selectedIndex;
	var distunitsvalue = form.distunits.options[i].value; 
	var j = form.speedunits.selectedIndex;
	var speedunitsvalue = form.speedunits.options[j].value;
	//  convert time to seconds
	var temp = ((parseFloat(form.hourvalue.value) * 3600) + (parseFloat(form.minutevalue.value) * 60) + parseFloat(form.secondvalue.value));
	//  calculate speed
	form.speedvalue.value = ((form.distvalue.value * distunitsvalue)  / (temp * speedunitsvalue)); 
	return true;
}
function clearcell(cell) {
	cell.value = "";
	return true;
}