See fig. 46 p. 171 A Collector's Guide to Fans over the Ages, Bertha de Vere Green: "illustrated in Harmsworth London Magazine, 1901 at six o'clock in the morning and in the evening, the fan would be wide open and a serpent fixed by its tail to the velvet (backing) would point the hour with its tongue. Immediately after six oclock, the fan suddenly closes, the serpent still pointing to six, but it would then be the figure on the right hand side of the fan. The pivot of the fan was rotated by clockwork driving a rack and pinion controlled by a snail-shaped cam, so allowing the fan to open gradually as the hours progressed. One of these clocks is to be seen in the Ilbert Collection (British Museum)"