By 1887, heliographs in use included not only the British Mance and Begbie heliographs, but also the American Grugan, Garner and Pursell heliographs. The Grugan and Pursell heliographs used shutters, and the others used movable mirrors operated by a finger key. The Mance, Grugam and Pursell heliographs used two tripods, and the others one. The signals could either be momentary flashes, or momentary obscurations.^[25] In 1889, the US Signal Service reviewed all of these devices, as well as the Finley Helio-Telegraph,^[25] and finding none completely suitable, developed the US Signal Service heliograph, a two-tripod, shutter-based machine of 13 7/8 lb. total weight, and ordered 100 for a total cost of $4,205.^[26] In 1893, the number of heliographs manufactured for the US Signal Service was 133.^[27]