I am recently trying the contract. Firstly, I use the stimulate functions on exchange. I open 2 orders at the same time, one for increased and one for decrease. When we have the sense from marketing place about the price, we can actually trade in the real market. As a sequence, it is hard to lose both sides.

By the way, when it is obverse to see the increase or decrease, I don't have to open for both sides. Hope this idea helps you.