Normally, when one writes a technical report, one writes about the historical background of the particular subject. This provides some continuity between the current state-of-the-art and what preceded it.
For example, if one was to write a paper on Ge-Li detectors (a type of solid state detector), one could also write on other solid state detectors or radiation detectors in general.
Great examples are found in patent applications. Part of the requirement of a patent is to present what was done in the past (BACKGROUND OF THE INVENTION or PRIOR ART) in the relevant class (or subject). The idea is to show that one is familiar with the subject and that one is aware that one's idea is new (or novel).
See for example - [URL [Broken] nuclear radiation detector with deep junction and radial field gradient[/url] or
search at www.uspto.gov for US Patent - 4,157,559. Just enter patent number.