Abstract: A calculator device for an electronic photoflash system in which a photosensor receives light reflected back from the scene being photographed and generates an electrical signal for providing termination of the flash upon sensing a predetermined amount of light. The light received from the scene is reflected from either of two surfaces having different light reflectivities, prior to receipt by the photosensor. The pair of surfaces are carried by a slidable member and selectively positionable at the point of light reflection in accordance with the selection of indicia carried on the front side of the member, by movement of the same by the photographer.