A session automatically starts all devices at the same time when you start an operation in most cases. You must configure them to start synchronously when devices are not on a single chassis and do not share a clock. If you have not configured synchronization on such devices, the start operation reduces the latency between devices, running them very close together to achieve near-simultaneous signals. However, devices are automatically and perfectly synchronized in the session if they are:
Subsystems on a single device in the session. This synchronizes your analog input, analog output, and counter input channels.
Modules on a single CompactDAQ chassis in the session.
PXI modules synchronized with a reference clock on a PXI chassis. For perfect synchronization, you must share a trigger as well. See Acquire Synchronized Data Using PXI Devices for more information.