When you sound the advance, the camps that lie on the east side shall then begin their journey.
Numbers 10:5
Surrounding context
10:4 But if they blow only one, then the leaders, the heads of the divisions of Israel, shall gather to you.
10:5 When you sound the advance, the camps that lie on the east side shall then begin their journey.
10:6 When you sound the advance the second time, then the camps that lie on the south side shall begin their journey; they shall sound the call for them to begin their journeys.