Check and refine the beam position

Since at this stage you can only look at angles between different nrlvs (and ndlvs), correct values for the crystal to detector distance and the beam position are crucial for successful indexing. To check the beam position:

• Display the conics at the top of the list of ndlvs with a reasonable small value of on the image using:

  
  
           show ndlv 1
  
  

  and check if these conics look like proper ellipses/hyperboles/etc.
• If a large number of conics has wrongly assigned spots, you have to refine the beam position, using the correct conics:

  
  
           calc beam 1 2 4 5 8 9 11
  
  

  If the beam position changes significantly, you should rerun NODIRAX ( run nodirax), check and, if necessary, refine the beam position again.
• The beam position can also be checked by using the gnomonic projection, show gnom dist. Spots lying on a conic in the Laue pattern will form a straight line in the gnomonic projection. Curving of these lines indicates an error in the direct beam position. You can try to optimize the beam center manually using this projection.