Yes. The 26M speed indicator is indeed reading water speed, independent of the gps-based chartplotter on board. In the Salish sea – I am based on the Saanich Peninsula – tidal currents through the various channels will affect water-based speed indicators. Nevertheless, I would expect more consistency between speed estimation methods. My tablet covers three different satellite-based position indicating services, including Galileo, the latest and most accurate at a claimed 1m resolution. Clearly more research is needed as different software will affect the interpretation of satellite-based methods. Topography/altitude, however, is not a confusing issue at sea level. I will try testing different software programs at constant speed with the tablet.