The Sekonic SE RT GX Transmitter is a user replaceable radio module that fits neatly next to the batteries in the SPEEDMASTER L 858D Light Meter. Upgrade your L 858D's firmware via Data Transfer Software, and you are ready to go. This transmitter offers wireless radio flash triggering of Godox compatible flashes . Sekonic's mission is to enable image makers to craft great light in every image, and the Sekonic RT GX simplifies the process. It helps you quickly dial in your lighting recipe to get to your final image with exacting precision . Full radio compatibility 32 channels (1 32), 16 groups (A F,0 9) and Wireless ID's to remotely trigger your Godox compatible lights up to 100ft (30 meters) away .