Dictionary:Roll on (roll off)

Acquiring data at the beginning (or end) of a seismic line where the stack multiplicity gradually builds up (or drops off) to that nominal for the line.

The term roll comes from a mechnical switch known as a roll switch (rota-long by I/O was common) that allowed one to add more active receiver stations as the source locations got further from the edge of the seismic program. This is unlike walk on where the roll switch remained constant until the shooter had walked into the nominal geometry location whereas the observer began rolling the spread via the roll switch.