[GSAS-II] oddities in hexagonal cell

[davide levy]

Hi, 
I refining a rhombohedral cell with hexagonal setting and I saw that the a
and b cell edges have same value but different sigma. Why ? 
Davide 
Reciprocal metric tensor: 

  names :            A11            A22            A33            A12
A13            A23

  values:    0.054780220    0.054780220    0.003540059    0.054780220
0.000000000    0.000000000

  esds  :    0.000002049                   0.000000214


 New unit cell:

  names :           a           b           c       alpha        beta
gamma      Volume

  values:    4.933527    4.933527   16.807176     90.0000     90.0000
120.0000     354.275

  esds  :    0.000123    0.000031    0.000508      0.0000      0.0000
0.0005       0.010

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