The dependency of the capacity on height was approximately given by Heron, a 1st-century engineer. He is credited with a number of formulae, all called "Heron's formula." As far as pottery is concerned, he divided pots into spheroid and pithoid, all the larger ones being the latter type, taking this classification from work done previously and appearing in the writings of Archimedes. The volume of a pithoid, which can be either a pithos or an amphora, is dependent, he asserts, on 11/14 of the product of the height and a number representing a squared average of minimum and maximum diameters.