Telling the time.

In my early childhood, this was by counting how many times it took blowing on a dandelion seed head before it was bald, or, 3600 x the duration of 9,192,631,770 (cycles) of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.
It was 3 o'clock when I took this. 

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