Abstract: An apparatus and method for monitoring the internal pressure or vacuum in a sealed container is provided which measures the amount of deflection of a flexible wall of the container as a function of the internal pressure. The apparatus provides a first electrical signal representative of the distance between a first point on the flexible wall and a first sensing means and a second electrical signal representative of the average of the distances between at least two other points of the flexible wall and second sensing means. The two signals are compared and a third signal indicative of the deflection of the flexible wall is provided.