The first operation is to select in the current index the calibrator observations performed during the time period when calibration is needed, and to plot the visibilities after having selected the baselines, side bands and/or subbands needed. This is done via SET BASELINES , SET BANDS , SET SUBBANDS commands. Time should be specified as X axis and amplitude as Y axis (in SET MODE TIME, of course).
Then a calibration curve is determined by command SOLVE AMPLITUDE .
It forces SET AMPLITUDE ABSOLUTE KELVIN to determine the
calibration curve 
which is then in memory.
For the type of curve (splines, breaks, polynomials), SOLVE AMPLITUDE behaves as the the SOLVE PHASE command applies.