is provided an opaque screen 13 having a transparent window 14 which extends over only that portion of the sweep of pointer 11 which corresponds to cruising operation of the vehicle oscillations of pointer 11 in idling or deceleration of the vehicle are made invisible by opaque portion 12 of the screen and oscillations of pointer 11 during abrupt acceleration of the vehicle are made invisible by opaque portion 13 of the screen in the embodiment illustrated there is provided fluid switch means 15 which is arranged between intake 1 and instrument 6 in passage 4 which connects the bourdon tube 5 to the atmosphere when the piston 16 is in a neutral position as shown so that pointer 11 is outside window 14 when the transmission of the vehicle is placed selectively in its highest speed spring 17 which is attached to the transmission shift lever at its left hand end in the figure draws valve 18 to the left thus connecting instrument 6 to the negative pressure of the intake 1 thus in accordance with this embodiment the instrument 6 operates only when the vehicle is in its highest speed the arrangement shown in the drawing simplifies the instructions to be given to the vehicle operator for effecting fuel economy he should try to keep the instrument pointer 11 within.