means and method are disclosed for determining the fluid content within a large pressure vessel , without penetrating the vessel . strain gauges are located at the weight - bearing support structures of the vessel , whereby calibrated differences in the weight of the empty vessel and the vessel as measured during operation gives a direct indication of fluid content . preferably , the strain gauges are associated with strain amplification elements or shims , which are interposed between mating surfaces of the vessel support and its base . the stress amplification element has a smaller area of contact with the support member than with the base , providing an effective higher coefficient of elasticity than that of the support member . in one embodiment , the strain gauge is connected to a bolt which tightly secures the vessel support to its base .