Before revision: They are a set of two charts per included geometry introduced in 1947 by M. P. HeislerTransactions ASME, 69, 227-236 , 1947 which were supplemented by a third chart per geometry in 1961 by H. Gröber.
After revision: They are a set of two charts per included geometry introduced in 1947 by M. P. HeislerTransactions ASME, 69, 227–236 , 1947 which were supplemented by a third chart per geometry in 1961 by H. Gröber.