Abstract: Methods and apparatus for measuring a non-thermal physical parameter with temperature sensitive elements impart a predetermined temperature sensitive elements, while measuring the physical parameter therewith. The same termperature-sensitive elements are employed for effecting a measurement of environmental temperature variation, and such temperature-sensitive elements are restored to their predetermined temperature in response to that measurement of environmental temperature variation effected with these temperature-sensitive elements.

Abstract: An analog to digital converter apparatus arranged to convert a plurality C (=4) of different input signals to digital representations thereof. The apparatus comprises a multiplexer arranged sequentially to couple each of the 4 input signals to a fast a-to-d converter (such as a successive approximations converter) at a rate such that each input signal is coupled N (=8) times in a period M (=20 m secs) of an a.c. series mode interfering signal (at 50 Hz) and at equal time intervals M/N (20/8=2.5 m secs). The N (=8) digital values of each input signal are averaged to provide at the end of a conversion period a digital value for each of the 4 input signals (C) which is the mean magnitude of the signal during the 20 m sec period (M).

Abstract: Apparatus suitable for use as a hydrostatic pressure standard comprises a vertically-mounted container charged with a predetermined amount of a liquid having a low-vapor pressure, such as an hydraulic oil, to provide a predetermined pressure head at a port at the lower end of the container. The container is provided at its upper end with a closure in the form of a variable volume device which is so arranged that the pressure in the space within the container above the liquid is maintained substantially equal to the external, e.g. atmospheric pressure. A system for determining the mass of a liquid in a tank and embodying two such pressure standards is also described.

Abstract: Apparatus for determining the position on a plane surface where a beam of light strikes the surface in relation to a datum position. In one embodiment the apparatus comprises a liquid crystal device having a common, transparent electrode on one surface and a plurality of spaced, parallel, segmental, transparent electrodes on the other surface to define a corresponding plurality of liquid crystal cells. Means is provided for changing the light-transmission characteristics of the liquid-crystal cells in a predetermined sequence from a datum position.