function changeDimension() {
	var inputs = document.getElementsByTagName("input");
	
	for (var i=0; i<inputs.length; i++) {
		if ((inputs[i].getAttribute('type')=='checkbox') && (inputs[i].getAttribute('id')=='unittype4')) {
			inputs[i].onclick = function() {
				if (this.checked) {
					setDimenstion("acres");
				} else {
					setDimenstion("sq ft");
				}
			}
		}
	}
}

function setDimenstion(dimension) {
	var dimselect = document.getElementById("dim");
	
	if (dimension=="acres") {
		dimselect.selectedIndex = 2;
	} else {
		dimselect.selectedIndex = 1;
	}
}

function addLoadEvent(func) {
    var oldonload = window.onload;
    if (typeof window.onload != 'function') {
        window.onload = func;
    } else {
        window.onload = function() {
            oldonload();
            func();
        }
    }
}

addLoadEvent(changeDimension);