To compound this problem, several researchers have examined the calibrations and power levels of ultrasound machines being used in clinical practice and reported large deviations in the power levels, which they attributed to poor calibration.6–11 Therefore, the purpose of our study was to examine 11 transducers from 6 manufacturers (n = 66 transducers) to determine the level of variability in ERA, power, and SAI for both intramanufacturer and intermanufacturer comparisons. These data may add perspective to the discrepancies in tissue heating that have been previously reported