Allow the polarsation correction to be completely disabled

1 files changed, 3 insertions, 1 deletions

diff --git a/doc/man/process_hkl.1 b/doc/man/process_hkl.1
index d01cfc5d..1d73963d 100644
--- a/doc/man/process_hkl.1
+++ b/doc/man/process_hkl.1
@@ -86,7 +86,9 @@ Use \fBpartialator\fR if you need more advanced merging techniques.
 .PD 0
 .IP \fB--polarisation=\fItype\fR
 .PD
-Specify the polarisation of the incident radiation.  \fItype\fR can be \fBhoriz\fR, \fBvert\fR or \fBnone\fR to indicate 100% polarisation of the electric field in the horizontal plane, vertical plane or completely unpolarised radiation respectively.  Alternatively, \fItype\fR can be a direction followed by a percentage polarisation fraction.  For example, \fB45deg90\fR means that 90% of the radiation is polarised with its electric field in a direction 45 degrees from horizontal, and \fB10deg100\fR means that all the radiation is polarised at 10 degrees from horizontal.  The angle is specified clockwise from horizontal as viewed along the beam direction, i.e. as shown by \fBhdfsee\fR.  The beam is unpolarised when the fraction is 50% (equal parts of the radiation have their electric field in the specified plane).  If the polarisation fraction is 100%, it can be omitted.  For example \fB10deg\fR or \fBhoriz\fR.
+Specify the polarisation of the incident radiation.  \fItype\fR can be \fBhoriz\fR or \fBvert\fR to indicate 100% polarisation of the electric field in the horizontal plane or vertical plane respectively.  Setting \fItype\fR to \fBnone\fR completely disables the polarisation correction (see the note below).  Alternatively, \fItype\fR can be a direction followed by a percentage polarisation fraction.  For example, \fB45deg90\fR means that 90% of the radiation is polarised with its electric field in a direction 45 degrees from horizontal, and \fB10deg100\fR means that all the radiation is polarised at 10 degrees from horizontal.  The angle is specified clockwise from horizontal as viewed along the beam direction, i.e. as shown by \fBhdfsee\fR.  The beam is unpolarised when the fraction is 50% (equal parts of the radiation have their electric field in the specified plane).  If the polarisation fraction is 100%, it can be omitted.  For example \fB10deg\fR or \fBhoriz\fR.
+
+Note that \fB--polarisation=none\fR is not the same as, for example, \fB--polarisation=vert50\fR.  In the first case, the polarisation correction will be completely disabled.  In the other case, the incident beam will be unpolarised, but the polarisation of the diffracted radiation will still be corrected for (the factor of (1+cos^2(2theta))/2 or, equivalently, (2-sin^2(2theta))/2).
 
 The default is \fB--polarisation=horiz\fR.