Sciothericum telescopicum was a sundial (sciothericum) that incorporated a telescope (telescopicum) for greater accuracy in determining exactly when noon occurred.
It was invented by William Molyneux in Ireland in 1686.
[1] The device used a telescopic sight to determine the position of the center of the Sun relative to a double gnomon and could thus determine the time of noon to within 15 seconds.
The improved accuracy was important for geography, navigation and astronomy calculations.
[2][3]