Numbers 10:4-7

But if only one trumpet is blown, then only the leaders—the heads of the clans of Israel—must present themselves to you. “When you sound the signal to move on, the tribes camped on the east side of the Tabernacle must break camp and move forward. When you sound the signal a second time, the tribes camped on the south will follow. You must sound short blasts as the signal for moving on. But when you call the people to an assembly, blow the trumpets with a different signal.