Descriptions of similar water clocks are given in the "Pañca Siddhāntikā" by the polymath Varāhamihira (6th century AD), which adds further detail to the account given in the "Sürya Siddhānta".. Further descriptions are recorded in the "Brāhmasphuṭa Siddhānta", by the mathematician Brahmagupta (7th century AD). A detailed description with measurements is also recorded by the astronomer Lalla (8th century AD), who describes the "ghati" as a hemispherical copper vessel with a hole that is fully filled after one "nadika".