The calibration standards are not relative. International standards exist to which these machines are set, using an artificial ear. When calibrated to the same standard, audiograms are merely compared to each other vis-a-vis threshold and frequency. Even if two audiograms are set to different standards, the standards are not radically different from each other, and differ only in a few decibels. Note also that differences between audiograms for the same frequency must be more than 5 dB to be deemed significant.