function price_correct()
	{
	// this function updates the on-screen price (and shopping cart price) when an option with a price correction is selected
	// note that price corrections are concealed in the HTML of the product page using hidden variables.
	
	var optioncode = document.getElementById('options').options[document.getElementById('options').selectedIndex].value;
	
	// first see if there is a price adjustment for this option
	if (eval('document.getElementById(\'' + optioncode + '_price\')'))
		{
		// add the base price and price correction
		var newprice = parseInt(document.getElementById('base_price').value) + parseInt(eval('document.getElementById(\'' + optioncode + '_price\').value'))
		// set the new price
		document.getElementById('display_price').innerHTML = '£' + newprice;
		document.getElementById('PRICE').value = newprice;
		}
	else
		{
		// there's no price correction for this option, so make sure the base price is displayed
		document.getElementById('display_price').innerHTML = '£' + document.getElementById('base_price').value;
		document.getElementById('PRICE').value = document.getElementById('base_price').value;
		}
	}