Sekonic Transmitter Module RT-20PW for L-858D-U Speedmaster light meter. Used to trigger Pocket Wizard enabled receivers and lights. Standard CH1 to 32 Flash light triggering Zone: A to D (after CH17) ControlTL® CH1 to 20 Flash light output power control and modeling Zone: A to C lamp ON/OFF Note: The current and old transmitter (RT-32FCC, RT-32CE, RT-32N, RT-32CTL) are NOT compatible with L-858D.