Abstract: A device for the indication of dirt accumulation on an air intake filter by measuring the negative pressure in the clean air space of the filter, the device having a spring-biased diaphragm piston driving a pointer shaft by means of a bell crank with a gear segment, the pointer shaft carrying two diametrically oppositely arranged pointers with vertical and horizontal length portions moving in axial and radial portions of a pointer gap defined between the housing cover and an indicator dial carried by the cover. A ratchet mechanism serves to retain the pointer readout by blocking return movements of the indicator mechanism, the ratchet mechanism being releasable by means of a reset button on the cover of the device. The device is calibrated by means of an adjustable bell crank spring.