A commercial Electrical Aerosol Analyzer (EAA, TSI Inc. model 3030) was calibrated experimentally at three subambient pressures (i.e., 0.901, 0.878, and 0.853 atm). Each calibration resulted in a 19 x 11 response matrix and a size dependent sensitivity curve (pA/#/cm3). The results of the calibration were incorporated into a data reduction computer program for size distribution inversion. The accuracy of the calibration was tested by measuring the size distribution of a NaCl polydisperse aerosol at the three subambient pressures. All the tests gave good agreement in the inverted mean geometric diameter and geometric standard deviation of the aerosol number size distribution.