I suppose you meant ‘Equinox’ by terming it ‘Equonix’. If this is the case then, to best of my knowledge there isn’t any dispute over its ‘Precision’ as it is astronomical data, it is recorded for coming century and it falls on the calculated time and date every year. In 2012 Vernal equinox is on 20th March 2012 at 05:14 UT, and the autumnal equinox is on 22nd September 2012 at 14:49 UT. In Latin it literally mean aequus (equal) and nox (night), every time the Sun is at zenith over the Equator, the day and night are equal causing Equinox.