[1] = Synagoge delta313, Photius delta650; cf. (for the first gloss) Hesychius delta1903. Nouns in the accusative singular. The material stems from Homer, Iliad 10.562: to/n r(a diopth=ra stratou= e)/mmenai h(mete/roio, "(a scout sent forth) to spy upon our army"; cf. scholia to that passage and the gloss to\n skopo\n in Etymologicum Magnum 278.10. The rare, poetic word recurs in later Greek prose: see Agathias 2.2; and delta 1193. diopth\r is also considered as an equivalent of the Latin word tesserarius, denoting a messenger who distributed the watchword from the commander to the soldiers. This is the meaning implied by Plutarch, Galba 24: *ou)etou/rios kai\ *ba/rbios, o( me\n o)pti/wn, o( de\ tessera/rios: ou(/tw ga\r kalou=ntai oi( diagge/lwn kai\ diopth/rwn u(peresi/as telou=ntes ("Veturius and Barbius, the former "optio", the latter "tesserarius": so are called the soldiers in charge of the task of messengers, dia/ggeloi, and inspectors, diopth/res). However, a closer analysis of the occurrences of these terms suggest that we rather see "optio" as corresponding to the Greek diopth\r, while tesserarius is closest in meaning to dia/ggelos. The meaning of "secret intermediary or messenger" is attested for dia/ggelos (see Thucydides 7.73.3); moreover, one does not find for "tesserarius" any reference to the supervision or control tasks which seem to be required from diopth\r and its subsequent explanation oi)kono/mos. Conversely, this is a meaning frequently attested for "optio": a term indicating an assistant of the centurion, but explained in Latin glossaries as "dispensator, qui dispensat stipendia militum; praepositus eorum". Cf. also Procopius, History of the Wars of Justinian 3.17 o(s oi( e)pemelei=to th=s peri\ th\n oi)ki/as dapa/nhs: o)pti/wna tou=ton kalou=si *(rwmai=oi, "the supervisor to the household expenses: the Romans call him optio".
[2] For the use of diopth/r as a synonym of dio/ptra (see next note) see Aetius 16.105 (cited by LSJ s.v.).
[3] Better known as dio/ptra (cited at the end of the entry, and see delta 1195) and thoroughly described by Heron of Alexandria, this instrument was intended to determine lengths from a distance and extensively used on aqueduct building projects and by astronomers. The Suda apparently refers to a military use, to assess the height of fortifications: for similar instances cf. Polybius 8.37.2 and 10.45.6.