Left: Example of a daily light curve as will be measured by the LAT for 3C279 for a flare comparable to the brightest one detected by EGRET for this source. The red curve corresponds to the seed flux while the blue line segments are the results of the maximum-likelihood analysis. The inset displays the true F(E>1 GeV)/F(E<1 GeV) hardness ratios versus the measured ones. Right: On-source time necessary to measure the flux and the spectral index of a source at high galactic latitude with an accuracy of 10% and 5% respectively, as a function of the source flux. A photon spectral index of 2.0 is assumed.