Use "mean time" in a sentence

1. An amount of 60 calories per square centimeter must be received by the retina in a mean time of 2′′ 75 to obtain a destructive and non reversible photocoagulation.

Um eine destruktive und irreversible Photokoagulation der Netzhaut hervorzubringen, muß dieselbe im Mittel 60 Calorien per Quadratzentimeter in einer Zeit von 2′′ 75 erhalten.