Consider rule to require either both azimuth and dip on channels or neither. Current rule 320 requires seismic channels to have both, but preventing other channels from having just dip or just azimuth would be good.
Possible exception for vertical channels, dip exactly -90 or 90, where only dip is really needed.
See https://github.com/FDSN/StationXML/issues/154
Consider rule to require either both azimuth and dip on channels or neither. Current rule 320 requires seismic channels to have both, but preventing other channels from having just dip or just azimuth would be good.
Possible exception for vertical channels, dip exactly -90 or 90, where only dip is really needed.