Apparatus for displaying measurements; Apparatus for indicating measurements; Apparatus for surface measurements; Apparatus for the storage of physical measurements; Electrodes (other than medical) made from synthetic materials for the measurement of chemical compounds; Electrodes (other than medical) made from synthetic materials for the measurement of ions; Electronic measurement sensors; Measurement apparatus; Measurement apparatus for well testing; Measurement devices; Measurement instruments for use in oil exploration; Optical apparatus for measurement; Optical measurement apparatus; Pressure measurement apparatus; Pressure measurement tools; Sensors (measurement apparatus), other than for medical use; Gamma counters; Depth determination apparatus; Depth gauges; Indicators for indicating depth; Sensors for measuring depth