Abstract: An aircraft instrument responsive to altitude and airspeed change. The instrument includes a first pressure transducer responsive to the pressure change due to changes in the altitude of the aircraft and a second pressure transducer responsive to pressure change due to changes in the airspeed of the aircraft. The output of each transducer is amplified and uniquely combined to provide an electrical signal representative of the rate of climb of the aircraft. The instrument also optionally modifies the airspeed transducer output and combines the modified signal with the rate of climb signal to provide a signal representative of the vertical movement of air outside of the aircraft. Additionally, the instrument may optionally provide an indication whenever best speed to fly conditions exist.