The pressure sensor in the Aquadopp and Aquadopp Profiler is sampled 80 ms after the start of each sample interval. The lag between pressure and velocity depends on the measurement load since the velocity is the average of all pings we do. In wave applications the measurement load is always 100%, hence the averaged velocity value will be centered around the middle of the sample interval. Depending on the exact setup the actual lag will be approximately 420 ms for 1 Hz measurements and 170 ms for 2 Hz measurements (Aquadopp Profiler).