NB: there is a seamark building function of 'time_ball' that could be more-relevant/precise for the timeball on Flamsteed House than the current value of 'observation'.

I think a seamark building type of 'observation' might indicate a place that the sea is observed _from_, while vice-versa a timeball is observed from the sea.

Maybe sea observations do take place from Flamsteed House?  But the time ball itself I think is primarily a visual signal for seafarers.

Tagging ref: https://wiki.openstreetmap.org/wiki/Seamarks/Buildings#Functions