Keywords: class-average

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## Controls

There are several controls which ensures that user adds consistant spectra. The first ones raise errors which stop the averaging process:

- The position compatibility is checked according to the position matching rule (`SET [NO]MATCH`, or option `/NOMATCH` for command `AVERAGE`). Default is to match the positions with a 2 tolerance.
- The calibration compatibility is checked according to the beam efficiency and gain image ratio tolerances set by command `SET CALIBRATION`. Default is to check the beam efficiencies with a 0.02 tolerance, but not the gain image ratios.
- In the intersection mode (`SET ALIGN * INTERSECT`), an error is raised if the input abscissae ranges do not intersect.

There is also a serie of conditions under which user is warned about possible inconstent mix of spectra:

- for channel alignment of the input spectra (`SET ALIGN CHANNEL`), a difference in the reference channels, in the frequency resolutions, or in the sky frequencies raises a warning,
- for frequency alignment of the input spectra (`SET ALIGN FREQUENCY`), a difference in the velocity offsets raises a warning (this indicates a different matching between the frequency and velocity axes),
- for velocity alignment of the input spectra (`SET ALIGN VELOCITY`), a difference in the rest frequencies raises a warning (for the same reason).

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