3C286 is the (slowly-varying) flux-density standard to which all VLA measurements are ultimately referred. If the LST range of your observing run permits, observe 3C286 for a few minutes at each observing frequency and bandwidth combination that you use for the targets, Failing this, observe 3C48 or 3C147 instead (or consult with VLA staff about recent determinations of the amplitude gains of the antennas from other observations before finalizing your observing program). Do not simply take the most recent flux density for an arbitrary calibrator from the VLA Calibrator List. Many small-diameter sources that in this list because they are suitable for position and instrumental calibration are variable. The flux densities recorded in the VLA Calibrator List will rarely have been measured recently enough to determine the absolute flux-density scale for your observations; use them only to estimate the integration times needed to achieve the desired gain accuracy from your calibrator scans.