You do: that's the signal that's sent over in 5ms. You then combine it with the local price 5ms ago, and you can construct the exact same instruction the comput

You do: that's the signal that's sent over in 5ms. You then combine it with the local price 5ms ago, and you can construct the exact same instruction the computer in the center would have come up with 2.5ms ago, based on the price in both locations 5ms ago. Both sides can this way make identical decisions to eachother, at the same time, and identical to those that would have been made by a computer in the center.