When #welltest recorders are run into a well they are measuring pressure vs. time (Dp/Dt). Liquid levels can be observed based on changes in the slope. Approximate liquid levels can be calculated assuming a constant running speed (Dd/Dt). This is close enough to qualify pressure gradients and correction magnitude of the initial measured pressure (i.e. the measured pressure may be low due to a liquid column between recorder run-depth (RRD) and formation datum depth (MPP).
With recorders on bottom for a time it is important to note the trend. If pressures are still building, stabilized conditions have yet to be achieved. Pressures may drop if the zone is still over charged by a fracture treatment or kill fluid. Interference or communication may be identifiable. The best condition, for analytical purposes (#PTA), is a flat, stabilized, pressure trend yielding a valid estimate of initial or average reservoir pressure.