The Sekonic L-858D is equipped with the RT-GX transmitter module. The RT-GX is a user-replaceable radio module that fits perfectly alongside the SPEEDMASTER L-858D light meter batteries. This kit offers a fully integrated light metering workflow to Godox users, allowing them to effortlessly measure, control and analyze flash characteristics like never before. The Sekonic RT-GX simplifies the portrait lighting process, analyzing a scene and helping you quickly dial in your lighting recipe to arrive at your final image with pinpoint accuracy. Sekonic Speedmaster L-858D-U is the world's first multi-brand multi-function wireless shooting light meter. It is the first of its kind capable of metering flash duration and short flash bursts like those found in HSS (High Speed Sync) for precision flash control. Features. Full radio compatibility: The L-858D with RT-GX transmitter module allows you to call all 32 channels (1-32), 16 groups (AF,0-9) and wireless IDs to activate Remotely your Godox compatible lights up to 100 feet (30 meters) away. You can even wirelessly control the power of the modeling lights. HSS Flash MeasurementGodox users can now measure HSS power. There's no need to guess what your exposure is when using high-speed sync. Tell the meter your ISO and shutter speed, and it will do the rest. Next Level Flash AnalysisNow Godox users can more easily measure the