Sending Manual Messages to ROV2

Okay! I think that makes sense. What about situations where there is a 0 in the button field? Is zero mapped to going forward or is zero just a place filler here? This is an example I found from you on a different thread that has a zero in the button field:

# Send a positive x value for 5 seconds.
# http://mavlink.org/messages/common#MANUAL_CONTROL
i = 0
while i < 10:
        master.mav.manual_control_send(
            master.target_system,
            500,
            0,
            0,
            0,
            0)
        time.sleep(0.5)
        i += 1

sys.exit(0)