The IWC 77 is an open face calibre mechanical watch movement equipped with a Breguet hairspring. It features pallets and an impuls pin made of steel, and if equipped with 7 jewels. There are several similar calibres, such as 570, 571, 572, 573, 670, and 671, but the exact differences between them are not known. The movement is part of a series with 15.25 through 16.5''' sizes, and although only partially known details are available, other calibres within this series include 1, 510, 511, 515, 610, 611, 613, 1713, and 1815, as well as 2, 3, 530, 531, 630, 631, 633, and 4, 540, 541, 640, 641. The IWC 77 movement offers the following functions: stem wind and set, and sub second. It was primarily used during the approximate period of 1930.