Is the order of orientation of electron box diagrams meaningful or arbitrary? Here is my interpretation when asked to:


  By drawing arrows in the appropriate boxes, complete the outer electron structures for Cu and Cu2+




I had no problem in drawing out the electron structure, but am a little confused by the orientation of my arrows.  I understand that each normal box has to have arrows in opposing directions to represent the opposite spins on the electrons, but the mark scheme defines which way round they want them to go:



Source: OCR GCE Chemistry B F334 June 2011 Markscheme pg. 11 

Ordinarily I would have said that whether you go up or down first (or even consistently) is irrelevant and arbitrary, but the comment in the guidance 


  ALLOW single arrow in either direction


suggests to me that with the paired arrows, the order of directions matter.



Is there any chemical reason for putting the downwards spin arrow first?  I would happily accept by convention as a reason but I just want to be sure that I'm not missing anything chemically relevant.
Raise hell with the grader. There's no reason whatsoever for this answer to be rejected. A Google book search can substantiate your argument, and the first example from a textbook is actually in your order:

         

I think the guidance “allow single arrow in either direction” is not exclusive with “allow double arrows in either order”, and maybe only single arrows were explicitly mentionned because it was obvious to the writer that order in double arrows doesn't matter.