Changing the scan rate or ac amplitude has a large effect on calibration, as shown in Fig. 5. Note that the scan rate was altered by changing the scan time while keeping the start and end frequencies constant. Thus, a longer scan time will correspond to a slower scan rate. The slope obtained in the final correction step decreases nonlinearly with increasing scan time, and the intercept correspondingly increases. This can be accounted for by considering the amount of time each ion is at resonance during the scan, which increases with scan time for a constant start and end frequency, resulting in more rapid ejection relative to the length of the scan. Both curves level out because further increasing the amount of time that each ion is at resonance does not change the ejection time relative to the scan time (i.e. the optimum resonance time has already been attained). The slope and intercept decrease and increase, respectively, in an approximately linear fashion (Fig. 5(b)) when the ac amplitude increases. This result is the direct consequence of ions being ejected more swiftly when the ac amplitude is high. Fortunately, this can be automatically accounted for in the mass calibration algorithm by inputting the ac amplitude as a variable. Since the relationship between slope/intercept and ac amplitude is linear, a second correction slope and intercept may be incorporated.