Abstract: A display device having a photosensing function is provided. A display device having a biometric authentication function typified by fingerprint authentication is provided. A display device having a touch panel function and a biometric authentication function is provided. The display device includes a first substrate, a light guide plate, a first light-emitting element, a second light-emitting element, and a light-receiving element. The first substrate and the light guide plate are provided to face each other. The first light-emitting element and the light-receiving element are provided between the first substrate and the light guide plate. The first light-emitting element has a function of emitting first light through the light guide plate. The second light-emitting element has a function of emitting second light to a side surface of the light guide plate.

Abstract: At first, a stop valve is fully opened to measure a pressure value P1 on the downstream side of the stop valve 66 under this condition. Subsequently, a pressure value P2 on the downstream side of the stop valve is measured when the flow velocity of compressed air flowing through the stop valve is set to be the sound pressure while adjusting the opening degree of the stop valve. Further, a pressure value P3 on the downstream side of the stop valve is measured when an ON/OFF valve is turned ON to release the compressed air from a nozzle. The consumption amount Q of the compressed air flowing through a fluid-operated apparatus is calculated by a calculating unit on the basis of the pressure values P1, P2, P3 and an effective cross-sectional area Sn of the nozzle.