Internal strain-gauge balances are multi-dimensional force transducers widely employed in wind tunnels to obtain accurate aerodynamic force and moment data on an aircraft model. Balances are calibrated periodically to assure measurement accuracy. The calibration provides a mathematical model relating the forces applied to the balance and the output signal from the balance. Currently, there are multiple types of internal strain-gauge balances used in wind-tunnel testing as well as multiple methods by which balances are calibrated. Because of the differences in the hardware and methodologies used to calibrate a wind-tunnel balance, it is hard to quantify the differences seen between the calibration results. The purpose of this study is to understand how the calibration of a balance is affected by the calibration system. Additionally, the study examines how the performance of a balance changes over time from a calibration perspective. These differences are quantified across different types of balances and different types of calibration systems. The long-term study employs multiple rigorous statistical methods as well as statistical process control techniques to provide insight into the stability of a process over time
