Thanks Martyn, but I think the "1" is there for AutoStop. Here is my Python code: status = windll.ps5000a.ps5000aRunStreaming( ps5000a_handle, byref(sampleInterval), 3, 0, 1000, 1, 10, 0, sizeof(ChannelA)) Here is your "C" code: status = ps5000aRunStreaming(unit->handle, &sampleInterval, timeUnits, ...