Hi, I have a tRNA molecule and I would like to measure the angles between two nitrogenous bases. I created two planes, each for each base. When I select both planes, in order to measure the angles between them (Structure Measurements Axes/Planes/Centroids) I get following message: <type 'exceptions.UnboundLocalError'> Exception in Tk callback Function: <bound method SortableTable._browseCmd of <CGLtk.Table.SortableTable instance at 0x117990638>> (type: <type 'instancemethod'>) Args: ('1',) Traceback (innermost last): File "/Applications/Chimera.app/Contents/Resources/lib/python2.7/site-packages/Pmw/Pmw_1_3/lib/PmwBase.py", line 1747, in __call__ return apply(self.func, args) File "/Applications/Chimera.app/Contents/Resources/share/CGLtk/Table.py", line 1043, in _browseCmd self.userBrowseCmd(self.selected()) File "/Applications/Chimera.app/Contents/Resources/share/StructMeasure/Geometry.py", line 268, in _tableCB self.feedback(sels) File "/Applications/Chimera.app/Contents/Resources/share/StructMeasure/Geometry.py", line 113, in feedback diff = " ".join(words2[i:]) <type 'exceptions.UnboundLocalError'>: local variable 'i' referenced before assignment UnboundLocalError: local variable 'i' referenced before assignment File "/Applications/Chimera.app/Contents/Resources/share/StructMeasure/Geometry.py", line 113, in feedback diff = " ".join(words2[i:]) See reply log for Python traceback. I really don’t know how can I solve this problem.. I’d be really grateful if you could help me or give me some hints! thank you a lot Letizia