function toggle_units(form, units) {

	if(units == 'imperial') {
		
		document.forms[form].elements['AVBSM'].disabled = 1;
		document.forms[form].elements['AVBSI'].disabled = 0;
		
		document.forms[form].elements['PRESSUREM'].disabled = 1;
		document.forms[form].elements['PRESSUREI'].disabled = 0;
		
	} else {
	
		document.forms[form].elements['AVBSM'].disabled = 0;
		document.forms[form].elements['AVBSI'].disabled = 1;
		
		document.forms[form].elements['PRESSUREM'].disabled = 0;
		document.forms[form].elements['PRESSUREI'].disabled = 1;
		
	}
	
}