The air bearing balance described in this paper has been designed to support the dynamic force measurement requirements of Virtual Flight Testing. This balance, the first in a series, is a single degree-of-freedom air bearing spindle. The bearing gas film is instrumented with fast-response pressure sensors that enable the determination of forces and moments. The device thus permits the measurement of unsteady aerodynamic loads on spinning test articles. The balance also incorporates a supply of high pressure air, delivered to the model without friction, for pneumatic actuators or reaction control jets. Spin at up to 20,000 rpm is made possible with a brushless motor. This paper focuses on calibration properties of the balance, particularly the influence of rotation angle and spin rate on the calibration parameters. Combined linearity and repeatability errors less than 0.5% full scale can be achieved at a fixed angle. Spin rate and angle deviations introduce errors as large as 20%, but angle and speed curve fitting can remedy these variations to less than 1.5%.