The ROCOZ‐A radiometer measures ozone by long pathlength photometry in the stratosphere and lower mesosphere. After a rocket launch to an apogee of 70 km, the instrument measures the solar ultraviolet irradiance over its four filter wavelengths as it descends on a parachute. The fundamental values from ROCOZ‐A are ozone overburdens versus radar altitude from 53 to 20 km. The slope of these values gives ozone number density. At one standard deviation the repeatability of the ozone overburden measurements averages 2.4%. For ozone number density the repeatability averages 3.2% with a significant increase at altitudes below the ozone number density maximum. The accuracy limits for overburden and number density are estimated at 5–7%. With auxiliary measurements of pressure and temperature, ozone results are also produced in terms of ozone mixing ratio, albeit with a slight broadening of the estimated accuracy limits. The vertical response of ROCOZ‐A ozone measurements (full width at half maximum) is 4 km. The assembly of ROCOZ‐A profiles can be used to compare with measurements from each of the current NASA and NOAA satellite ozone instruments. In addition, the repeatability of ROCOZ‐A allows the use of this instrument as a transfer standard between satellite instruments with different fundamental ozone measurements.