Not "reflect" but "hold an impression." The Greek has no verb: Τοῦ ὅλου αἰῶνος καὶ τῆς ὅλης οὐσίας συνεχῶς TERMφαντασία — literally "of the whole age and the whole substance, a continual impression." Marcus prescribes not an act of thought but a sustained state — a permanently available picture against which everything else is seen. Both translators supply a verb ("contemplate"; Rogovin's «думай»), and the prescription turns into an exercise, whereas in the original it is rather a background of vision. The modernization restores the noun.

Two measures, not one. The EXERCISEview from above here is twofold, and this matters: every particular is measured both by οὐσία (substance) and by χρόνος (time). Against the substance of the Whole a single thing is a κεγχραμίς; against time, a τρυπάνου περιστροφή. One measure alone would not do: what is vast in bulk may endure, what is long may be huge. The two together leave no loophole.

Two images. κεγχραμίς is not simply "a little grain": it is the pip inside a fig — the small within the small. Long gives "a grain of a fig"; Rogovin generalises to «малое зерно». τρυπάνου περιστροφή is "the turn of a drill": not a span of time but a single rotation of a craftsman's bit, the least movement of a hand. Both images are taken from daily work, not from cosmology — and that is their force: the greatness of the Whole is measured by a fig-pip and the turn of a hand. Cf. 5.24; 6.36; 9.32. The governing discipline is assent, the sustaining one desire.