In documentary papyri, a horizontal bar placed above or next to the Greek letter(s) will indicate a numerical value. Here are some examples from the Oxyrhynchus collection.
1) P.Oxy. 3340.5 (Senatorial Proceedings): ις̄ β[ο]υ̣λῆϲ = day 16, (there being a meeting) of the senate
2) P.Oxy. 2596.6-7 (Letter from Sarapammon to Andronicus): ταρίχουϲ ε͞ καὶ καθαροὺϲ δ͞ … / χαρτάρια β͞ = 5 salty fishes and 4 fine loaves … / 2 pieces of papyrus
3) P.Oxy. 3084.5 (Letter of Heraclius to Themistocles): τῆι κ͞δ ἑϲπέραϲ = on the 24th at evening
4) P.Oxy. 3096.2 (Complaint of an Error in Records): ϛ͞ φυλῆϲ γ͞ περιόδου = sixth tribe, third cycle
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