Precision of light curve amplitude measurement, in units of the measurement quality for an infinitely deep reference, as a function of the number of epochs N_e used in the reference image. For each band, the spread at a given reference depth is due to redshift (0.75 <z< 1.55), and the effect increases with redshift. If all events were measured using 45 reference epochs (i.e. one season), the measurement precision would degrade by less than 10% relative to the chosen baseline, i.e. 60.