To illustrate the effect of transducer coupling force, the technique was applied to five navel oranges. Each of the oranges was selected to represent an extreme case, with varying sizes (77–96 mm average diameter), ages (0–2 weeks post-harvest) and peels which ranged from smooth to rough and porous. Ultrasonic measurements were taken on each orange with the transducer being pressed against the equator of the orange with forces varying from 25 N to 50 N in 5 N increments. For each applied force, four measurements were taken at equally spaced points around the equator of the orange and averaged.