If a variance array is present in the input file, the output variance of a polar bin is the mean of the variances of the image pixels within that bin. If input variances don't exist then the output variances are calculated from counting statistics.
NB: The algorithm used relies on the fact that the image pixels are square. If the pixels in the image are not square then the program prints a warning message and continues executing.
By default azimuthal distributions are taken such that looking right along the X axis is azimuth=0 and increase moving anti-clockwise. The initial position to call azimuth zero can be specified on the command line by AZSTART = 90, which means start from the North position.