function calculator() {
	document.getElementById('calculator').style.display = 'block';
	document.getElementById('sqr_metres').style.display = 'none';
}

function calculate() {
	document.getElementById('calculator').style.display = 'none';
	document.getElementById('sqr_metres').style.display = 'block';
	var aside = document.getElementById('a_side').value;
	var bside = document.getElementById('b_side').value;
	
	var total = aside * bside;
	document.getElementById('sqr_metres').value = total;
}