
To trade FOREX using this technique you need to know 3 pair movement - eur-usd, usd-chf and eur-chf. It is easier to be able to see all three pair movement in 1 window at the same time.
Understanding of basic pair movement and its correlation will help. Theoritically, people will say if you buy eur-usd and buy usd-chf at the same time, it is the same as you are buying eur-chf.
That is not right, you will understand better when you monitor these 3 pair movement pattern at the same time.