I have quantity boxes that I need to validate the min. qty for. I nearly have it working using the following code...

// Quantity Check - 10 Lengths
 			function check_qty() {
     		var qty=document.getElementById('min10').value;
     		if(qty<10) {
         		alert("Sorry but this product has a minimum order of 10 lengths. Please enter 10 or more in the quantity box.");
The URL for my test is http://shockproof.bpweb.net/UKHI/content/QTY_TEST.php

My problem is that when I add less that 10 into the first qty field it throws up alert and when I close it empties the field...ALL GOOD! Trouble is if I go down to the next product and add a number less that 10 I get the alert msg but the field does not clear once I clear the msg. I have also experienced it adding to basket on the second try even if you enter less that 10.

Am I missing something simple?? Any ideas!

Thanks in advance