Each dot is one daily percentage move in FRED’s USD-to-CAD exchange rate; the centerline and three-sigma limits come from all 399 moves shown. Of those, 393 stay inside as common-cause variation; six cross a limit and become signals to investigate, not proof of a cause. For cross-border food purchasing, reacting to every ordinary move is tampering: it adds decisions to noise and can make the process worse. Change the system for a verified cause; otherwise leave it alone.