Abnormal behavior of the nonlinearity parameter evaluated from static displacement generation based finite amplitude ultrasonic wave propagation experiments at low input amplitudes is considered. Systematic experiments have been conducted on various materials by selectively replacing the instrumentation used on the transmitter and receiver side to explore the plausible contributions from each of the equipment used. The cause of the abnormal variation is found to be due to the resolution of the digitizer. Our study suggests that high resolution digitizers should be used for making reliable measurements at low input amplitudes. © 2009 American Institute of Physics.