“…In a similar investigation conducted in Recife, PE, in northeastern Brazil, which used the same criteria for calibration error as that of our study, Costa et al found 12.7%, 25.3% and 10.1% tonometers with calibration errors at positions "0", "2", and "6", respectively (13) . In that study, it was observed that 25.3% of tonometers presented a calibration error, a quite (21) , still a quite smaller number than that found in the present study.…”