↩ 🔵 🔵 🔵 ❪✺❫ Temporal Concepts ○ ❪✺₁❫ Metrological Classes ○ ❪✺₁❫ Physical Classes ○ Time ⚪ Calendar ○꠹ Clock ○꠹ Date ○꠹ Day ○꠹ Timer ○꠹