The `i' key toggles between display of the total intensity (`I' in upper right corner of the display; observable portions of the 
-
tracks coloured green) and linear polarization (`P' in upper right
corner of the display; observable portions of the - tracks coloured
yellow and green). For polarization-sensitive VLBI observations, typically
both right- and left-circular polarization (RCP and LCP) are recorded at each
antenna, although it is still possible to obtain useful polarization
information if some antennas record only one circular polarization. The total
intensity - coverage will always be symmetric, but the linear
polarization - coverage will be symmetric only if both RCP and LCP have
been recorded at all antennas participating in the observations.