Abstract: Apparatus for detecting the magnitude of a property of a fluid including a body mounted on a torsion spring that is oscillated by a feedback of alternately an in-phase and an out-of-phase signal from an amplifier having a gain adequate to sustain the oscillations. If the in-phase signal has a period directly proportional to T.sub.n, the out-of-phase signal has a frequency directly proportional to f.sub.h, and the out-of-phase period is directly proportional to T.sub.h, then the magnitude of the property p is determined by the digital computation ofp = Kf.sub.h (T.sub.n - T.sub.h) - Bwhere K and B are constants. The property p may be any one of several properties including but not limited to viscosity.

Abstract: A vibration gravitometer having leaf spring vanes located in respective cells in a thermally conductive block. Each cell contains a different gas at ambient atmospheric temperature and pressure. One cell contains air, the other a gas, the gravity of which is to be monitored, "gravity" being defined as the ratio of the density of the gas to the density of air at the same temperature and pressure. The gravity of one specific gas of constant composition is a constant. The vanes are vibrated at the same or different frequencies dependent upon the air and gas densities. These frequencies are multiplied and combined in a digital calculator that utilizes a frequency-time reciprocal to divide. A readout circuit multiplies the output of the calculator by a constant of proportionality and indicates the gravity.