| CPC H01J 49/0027 (2013.01) [H01J 49/421 (2013.01)] | 17 Claims |

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1. A method of determining in a spectrometer an average frequency of a series of ion detection pulses during a measurement interval, the method comprising:
determining the duration of an auxiliary interval, wherein the auxiliary interval overlaps the measurement interval,
the auxiliary interval begins at the last pulse preceding the measurement interval, and
the auxiliary interval ends at the last pulse of the measurement interval;
determining the number of pulses during the auxiliary interval; and
dividing the number of pulses by the duration of the auxiliary interval so as to produce the average frequency.
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