The Nuraghic well of Santa Cristina, Sardinia has been regarded as a ritual monument built to receive moonlight on its water mirror at the time of the meridian passage of the moon when it reaches its highest point in the sky during and around the major northern lunistice. In this paper we investigate the precision that could have been achieved and conclude that the well could indeed have served as an instrument for measuring the lunar declination during half of the draconic cycle of 18.61 years.