calcodes are generated based on observing intents established during the SB creation. These intents are then passed along to the SDM data set. These are summarized easily in AIPS by typing:

>help calcode

Giving:

Help on CALCODE in AIPS version 31DEC10
CALCODE
Type: Adverb  (String*4)
Use:  This string is used to specify a desired calibration
      source code.
      '    ' => any calibrator code selected
      '*   ' => any non blank code (calibrators only)
      '-CAL' => blank codes only (no calibrators)
Null value: none

The VLA has attached meaning to letters as follows:

None = target source, or no potential calcode specified

Old style VLA (indicators of positional accuracy):
    A = positional accuracy <0.002  arcseconds
    B = positional accuracy  0.002 - 0.01  arcseconds
    C = positional accuracy  0.01 - 0.15  arcseconds
    T = positional accuracy >0.15  arcseconds

New style EVLA (indicators of scan intents):
    D = calibrator useful to determine Complex Gains
    E = calibrator useful to determine the absolute Flux Density
        Scale; typically only used for 3C48, 3C147, 3C286 (and 3C138,
        3C295)
    F = calibrator useful to determine the spectral Bandpass response
    G = calibrator useful to determine Polarization Angle
    H = calibrator useful to determine the instrumental Polarization
        Leakage
    I = calibrator for Complex Gain and Bandpass
    J = calibrator for Complex Gain and Polarization Leakage
    K = calibrator for Flux Density Scale and Bandpass
    L = calibrator for Flux Density Scale and Polarization Angle
    M = calibrator for Bandpass and Polarization Angle
    N = calibrator for Flux Density Scale, Bandpass and Polarization
        Angle
    O = calibrator for Complex Gain and Flux Density Scale
    P = calibrator for pointing observations
    Q = calibrator for Complex Gain, Flux Density Scale and Bandpass
    R = calibrator for Complex Gain, Flux Density Scale, Bandpass and Polarization Angle
    Y = recognised as calibrator source in the VLA catalog by the
        pipeline; only appears when no other calcodes are present and
        NOT an indication that this calibrator is useful at this
        frequency or in this array
    Z = any other non-Target combination of intents

Occasional VLBA:
    V = recognised as VLBI source in the VLBI "sched" catalog

Code   Gain Flux  BP Pang  P%
  D      X
  E           X
  F               X
  G                    X
  H                        X
  I      X        X
AIPS 1: ** press RETURN for more, enter Q or next line to quit print **
#
 autarch   AIPS (31DEC10)   2492     06-MAY-2010  14:50:41    Page    2
Help on CALCODE in AIPS version 31DEC10
  J      X                 X
  K           X   X
  L           X        X
  M               X    X
  N           X   X    X
  O      X   X
  Q      X   X   X
  R      X   X   X   X

The VLBA has attached different meanings on occasion as well to some
of the EVLA codes.

-- JosephMcMullin - 06 May 2010