A collection or string of 13 pearls weighting a Dharaṇa is known as Pikkā; one of 16 pearls of the same weight is known as Piccā; one of 20 pearls is known as Arghā; one of 25 is known as Ardhā , one of 30 as Ravaka; one of 40 as Siktha; one of 55 as Nigara : one of from 80 to 500 pearls is known as Cūrṇa .