The four exposure meters here are all actinometers relying on the time taken for a piece of sensitised paper to change tint in light compared against a fixed control tint, in order to determine the exposure. The Watkins Standard meter was originally introduced in 1890 and the Dial meter was introduced in 1900. The Snipe was a variant on the Dial meter. The Adams & Co. meter combined a stop watch with the actinometer.