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Università di Palermo, D.S.F.A., Sez.di Astronomia P.zza del Parlamento 1, 90134 Palermo, Italy.

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... error

We adopt as errors on our median zero point the semi-interquartile intervals.

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... effective

I.e. the area corrected for the regions removed around the troublemakers.

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... function

The function has been convolved with a boxcar filter in order to take into account the finite amplitude of the magnitude bins.

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