Using a Calendar Club voucher code is easy, all you have to do is:
Select the product and add it to the shopping basket.
Click the shopping basket icon on the top right-hand corner of the page.
Find and click on the "Voucher Code" box under the Sub Total tab.
Enter your discount code in the box and click on "Update".
You will see the discounted price under "Total Saved".
Click on "Checkout" and you're done.