The BaroTROLL Data Logger measures and logs barometric pressure and temperature, data needed to compensate for water level changes due to barometric fluctuations. Use this data logger with non-vented (absolute) Aqua TROLL 100/200 or Level TROLL 400/700 water level loggers, or use it with vented systems to calculate barometric efficiency. Baro Merge software handles the rest, automatically post-correcting water level measurements for you.