... processed1
At the moment, circular polarization can only be measured when using dual-beam data. 
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... sections2
It is hoped to rationalize the differences between these two modes in future releases. 
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... sky3
In the near infra-red flat-fields are normally taken on the night sky which at these wavelengths is bright enough to give a good signal to noise ratio. 
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... .sdf4
The double quotes are needed to prevent the asterisks being expanded by the shell. The expansion of these file templates is performed internally, within fits2ndf. 
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... application5
Once imported, the POLPACK extension is propagated through the entire data reduction sequence, with new items being added at various points to describe the intermediate stages of processing. 
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... process6
Rotation is currently only possible when processing single-beam data. 
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... above7
The final step - calculating the Stokes parameters - is optional. This allows POLKA to be used as a general purpose image alignment tool for non-polarimetric data. 
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... polarization8
POLPACK can currently only measure circular polarization for dual-beam data. 
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...etc.9
The sequence number added to the end of the file name is always one higher than in any existing files. 
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... gks74.ps.110
If you are unsure about which PostScript file is which, don't forget that you can examine the individual files using ghostview. 
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... file11
HDS container files can usually be identified by the fact they have a file type of .sdf. They can be used to store one or more standard Starlink NDF structures. 
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... parameters12
There is a fourth Stokes parameter, $V$, which is always zero for linearly polarized light, but is non-zero for circularly polarized light. 
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... axes13
The only exception is that when data is ``smoothed'' it is only smoothed in the two spatial axes - no smoothing occurs between spectral channels. 
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... co-variances14
Neither do they use the improved de-biassing technique described by Sparks & Axon. 
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... multiple15
Specified by POLCAL parameter NSIGMA. 
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