A majority of nuclear measurements involve digital pulse counting so that the associated instruments have many common functions. Further investigation reveals that these counting systems fall into two broad classes: Those in which all pulses exceeding a certain threshold are summed, and a more complex analyzing procedure wherein pulses must be classified according to amplitude or temporal distribution.In the former class are found the orthodox scalers, while the latter defines the pulse amplitude analyzers and other machines capable of yielding spectral distributions.It is found that such instruments may be synthesized from a common group of sub units, and these are outlined and listed on a functional basis.While the utility of the sub units is evidently determined by their versatility, they are in addition required to have high reliability in order that complex assemblies may give satisfactory service. Design for long life follows naturally from the latter consideration.The next section of the paper shows the manner in which the simpler instruments can be synthesized according to the proposed scheme and outlines the more complex automatic counting and analyzing systems to follow in later parts of the paper. In particular the construction of a range of scalers is illustrated and their performance specifications and photographs are shown.