function showSub(parentID, subID) {
// sub object
	subo = document.getElementById(subID);
	
// close all the subs
	document.getElementById('sub-milling').style.display = 'none';
	document.getElementById('sub-turning').style.display = 'none';
	document.getElementById('sub-engineering').style.display = 'none';
	document.getElementById('sub-vacuum').style.display = 'none';
	document.getElementById('sub-about').style.display = 'none';
	document.getElementById('sub-contact').style.display = 'none';

// state of sub object
	state = subo.style.display;

// open the correct sub
	if (state == 'block') {
		subo.style.display = 'none';
	} else {
		subo.style.display = 'block';
	}
}