The Southern Hemisphere Additional Ozonesondes (SHADOZ) project has collected more than 3000 ozone profiles from 14 tropical and subtropical sites using balloon-borne electrochemical concentration cell (ECC) ozonesondes flown with standard radiosondes. Published analysis of ozonesonde precision from SHADOZ profiles measured in 1998--2000 revealed that variations in ozonesonde technique might cause small station-to-station biases in the total ozone measurement. We present further evaluation of imprecisions and accuracy based on 1998--2004 SHADOZ data, results from laboratory simulations of ozonesonde flights, and a revised back-scattered ultraviolet algorithm, the TOMS version 8, 2004 release. The laboratory studies used standard ECC ozonesondes in a flight simulation chamber to evaluate techniques used at SHADOZ stations. Ozone deviations from a standard ozone instrument in the chamber tests resemble those of SHADOZ station data relative to a SHADOZ-defined climatological reference. Certain systematic variations in SHADOZ ozone profiles are accounted for by differences in solution composition, data processing, and instrument manufacturer. When SHADOZ total ozone column amounts are compared to the new TOMS algorithm, discrepancies between sonde and satellite decline 1--2 percentage points on average, compared to version 7 TOMS.