Now you can monitor barometric pressure in real time to match your fishing tactics to changing weather conditions. See increasing or decreasing barometer trend and digital readout on your sonar screen. Access full screen, easy to understand barometer trend for past 12 hours. Always have the latest information - WeatherSense internal battery & smart monitoring system independently logs the last 12 hours of the information, even if your Matrix unit is not connected. Simple plug & play operation. Compatible with Matrix 10, 15, 20, 25, 27, 35, 37,47 3D, 55, 65, 67, 77c, 87c. 900 Series: 931c, 931c DF, 937c Combo, 937c DF Combo, 947c 3D Combo, 981c SI & 987c SI Combo.