Derived metrics - fix last TODO
Derived metrics - fix last TODO

Problem with matching instances for binary operators when the number
of instances (and hence the instance identifiers) do not match between
the left and right operands.

prasincs/pcp,mbaldessari/pcp,wuliming/pcp,tjanez/pcp,aeg-aeg/pcpfans,adfernandes/pcp,adfernandes/pcp,ryandoyle/pcp_original,ryandoyle/pcp_original,wuliming/pcp,mbaldessari/pcp,aeg-aeg/pcpfans,tjanez/pcp,tjanez/pcp,prasincs/pcp,wuliming/pcp,andyvand/cygpcpfans,tjanez/pcp,aeg-aeg/pcpfans,andyvand/cygpcpfans,mbaldessari/pcp,andyvand/cygpcpfans,wuliming/pcp,edwardt/pcp,ryandoyle/pcp_original,aeg-aeg/pcpfans,andyvand/cygpcpfans,tjanez/pcp,edwardt/pcp,ryandoyle/pcp_original,edwardt/pcp,andyvand/cygpcpfans,mbaldessari/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,tjanez/pcp,prasincs/pcp,andyvand/cygpcpfans,mbaldessari/pcp,prasincs/pcp,aeg-aeg/pcpfans,adfernandes/pcp,edwardt/pcp,aeg-aeg/pcpfans,edwardt/pcp,edwardt/pcp,tjanez/pcp,prasincs/pcp,wuliming/pcp,aeg-aeg/pcpfans,wuliming/pcp,prasincs/pcp,mbaldessari/pcp,prasincs/pcp,ryandoyle/pcp_original,adfernandes/pcp,wuliming/pcp,edwardt/pcp,andyvand/cygpcpfans,prasincs/pcp,adfernandes/pcp,wuliming/pcp,edwardt/pcp,andyvand/cygpcpfans,ryandoyle/pcp_original,ryandoyle/pcp_original,tjanez/pcp,aeg-aeg/pcpfans,ryandoyle/pcp_original