An ancient Greek optical surveying instrument similar to a modern theodolite, used for measuring angles and distances in land surveying and astronomy.
From Greek 'dioptra,' literally 'that which sees through,' an ancient instrument name preserved in English and referring to its function of sighting through apertures.
The dioptra was invented by Hero of Alexandria around 1 CE and was so advanced that surveying instruments didn't significantly improve until the telescope was invented—ancient engineers used this to build aqueducts with incredible precision over miles.
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