I think the first Pickup machine that record dictates the BPM (so it gets to be the Master) the other Pickups are Slave to the Master.
Keep in mind that the Pickup calculates automaticaly the bpm as soon as you close your measure/bars…so -actually- it is the sequencer that get synced with the pickup.
Hope this was some answer you were looking for…
Otherwise: pg 55 of the manual
MASTER AND SLAVE PICKUP MACHINES
The first Pickup machine that records a loop acts as the master. The BPM of the Octatrack will automatically change according to the calculated BPM of the recorded loop. If Pickup machines are assigned to other tracks, the loops they record will be slave loops. The length of these loops can be dependent of the length of the master loop. If the LEN parameter of a slave Pickup machine is set to X1, the loop that machine will record will have the same length as the master loop. It will also force the slave loop to be in phase with the master loop. If set to X2, the slave loop will be double the length of the master loop. If playback of all Pickup machines is stopped, the first Pickup machine that records a new loop will be the new master.
The master/slave relation is visualized by the track icons. Two pixels located at the top left side of the “P” indicate a master Pickup machine. Two pixels to the bottom left indicate a slave Pickup machine.
In the illustration above, the leftmost track icon depicts a master Pickup machine while the right icon shows a slave Pickup machine.