Method A = Refractor, micrometer
Method B = Reflector, micrometer
Method C = Comparison image micrometer
Method D = Heliometer
Method E = Visual interferometer
Method F = CCD astrometry
Method G = Photographic, with astrograph
Method H = Photographic, with medium or long-focus technique
Method I = Transit method
Method J = Occultation binary
Method K = Long baseline interferometer
Method L = Electronographic camera
Method M = Meridian circle
Method N = Visual measures with a double-image micrometer
Method O = Photographic, with ocular enlargement
Method P = Photoelectric phase-grating interferometer
Method Q = HST (FGS, WFPC, NICMOS, etc.).
Method R = RGO use of micrometer plus comparison image micrometer on same star
Method S = Speckle interferometry
Method T = Hipparcos type observation - aperture reflects Rayleigh limit at V
Method U = Adaptive Optics
Method V = Photocell with diaphragm in focal plane
Method W = Area scanner
Method X = Visual estimate made with an objective grating
Method Y = Wedge photometer
Method Z = Visual photometry with a double-image or polarizing photometer