Understanding parallax

By parallax means change direction to an object to a moving observer traveling the direction perpendicular to the observed.
Parallax is used in geodesy and astronomy, to determine the distance to an object inaccessible.
The analog indication of measurement devices, parallax is given by the observer eye position and dial pointer to the device, contributing to errors of measurement.
Measurement is the process of obtaining experimentally one or more values of size attributable to a reasonable size. Science of measurement is metrology. Measurement is a process of determining the size (large) size of a physical quantity such as length or mass, in relation to a unit, such as meter and kilogram.
For other areas, such as social sciences, the concept of measuring previous exposure can not be implemented because there is no unit in the social sense. However measurements are made even there but defining the measurement is then an assignment of numbers of objects, phenomena, events.