[gnuastro-commits] master 56f9de0: Book: edits in the description of Fits's --verify option

[Mohammad Akhlaghi]

branch: master
commit 56f9de0fe24c22f66e1b63e789d94045c20e9d37
Author: Mohammad Akhlaghi <mohammad@akhlaghi.org>
Commit: Mohammad Akhlaghi <mohammad@akhlaghi.org>

    Book: edits in the description of Fits's --verify option
    
    Until now, there were a few typos in the description of these option and
    also the description of CHECKSUM and DATASUM could be improved.
    
    With this commit, those edits and clarifications have been made.
---
 doc/gnuastro.texi | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/doc/gnuastro.texi b/doc/gnuastro.texi
index 589c166..35f9ff6 100644
--- a/doc/gnuastro.texi
+++ b/doc/gnuastro.texi
@@ -9415,16 +9415,16 @@ Since its not too long, you can also simply put the 
variable values of the first
 @cindex @code{DATASUM}: FITS keyword
 @cindex @code{CHECKSUM}: FITS keyword
 When nothing is given afterwards, the header integrity keywords @code{DATASUM} 
and @code{CHECKSUM} will be calculated and written/updated.
-This is calculation and writing is done fully by CFITSIO.
-They thus comply with the FITS standard 
4.0@footnote{@url{https://fits.gsfc.nasa.gov/standard40/fits_standard40aa-le.pdf}}
 that defines these keywords (its Appendix J).
+The calculation and writing is done fully by CFITSIO, therefore they comply 
with the FITS standard 
4.0@footnote{@url{https://fits.gsfc.nasa.gov/standard40/fits_standard40aa-le.pdf}}
 that defines these keywords (its Appendix J).
 
 If a value is given (e.g., @option{--write=checksum,MyOwnCheckSum}), then 
CFITSIO won't be called to calculate these two keywords and the value (as well 
as possible comment and unit) will be written just like any other keyword.
-This is generally not recommended, but necessary in special circumstances (for 
example when the checksum needs to be manually updated).
+This is generally not recommended since @code{CHECKSUM} is a reserved FITS 
standard keyword.
+If you want to calculate the checksum with another hashing standard manually 
and write it into the header, its is recommended to use another keyword name.
 
-@code{DATASUM} only depends on the data section of the HDU/extension, so it is 
not changed when you update the keywords.
-But @code{CHECKSUM} also depends on the header and will not be valid if you 
make any further changes to the header.
+In the FITS standard, @code{CHECKSUM} depends on the HDU's data @emph{and} 
header keywords, it will therefore not be valid if you make any further changes 
to the header after writing the @code{CHECKSUM} keyword.
 This includes any further keyword modification options in the same call to the 
Fits program.
-Therefore it is recommended to write these keywords as the last keywords that 
are written/modified in the extension.
+However, @code{DATASUM} only depends on the data section of the HDU/extension, 
so it is not changed when you add, remove or update the header keywords.
+Therefore, it is recommended to write these keywords as the last keywords that 
are written/modified in the extension.
 You can use the @option{--verify} option (described below) to verify the 
values of these two keywords.
 
 @item datasum