Models for measuring the liquid level in the tank of rocket carrier

The models for measuring the level of a viscous incompressible fluid in the tank by liquid level in the measuring tube are considered. The tank is in the gravitational field and the level of liquid inside varies according to some law. The base model is the first boundary value problem for nonlinear integro-differential equation of parabolic type. The empirical model is Cauchy problem for nonlinear ordinary second order differential equation. It is numerically founded that for linear time-decreasing level of fluid tank fluid level in the measuring tube oscillates about level in the tank with damping amplitude.