As you already have a BigDataBall account, you can activate your 20% discount when you want to buy historical datasets or one-off in-season plans.
Follow these steps to get the 20% discount applied:
1) Make sure you already added historical datasets or one-off in-season plans to your shopping cart.
2) Click this link to activate your discount.
3) In the cart page check out the applied discount.
4) You can now proceed to the checkout page and complete your purchase.
Note that only historical datasets and the one-off in-season plans are eligible for the member discount.