Measurement is the assignment of numbers to objects or events and is a cornerstone of most natural sciences, technology, economics and quantitative research in social sciences.
Any measurement of an object can be judged by the following criteria values: level of measurement (which includes magnitude); dimensions (units); and uncertainty.
These criteria enable comparisons between different measurements and minimisation of confusion. The science of measurement is called metrology.
This Weston Electrical Instrument Co, Newark, New Jersey, USA voltmeter has a certificate number 2056. Its full title is a Weston standard portable alternating & direct current voltmeter.
The certificate, pasted into the wooden box housing the voltmeter says that it was standardized at 101 St Martin's Lane, London on 11 November 1898 and was certified by A C Heap.
A panel on the voltmeter says that it was patented August 5 1890, no. 433637, reissued June 28 1892, no. 11250 and patented 11 November 1890, no. 440289 and no. 440290.