These two variables (CmG or CmN) can be seen in figure 4 in two documents (and figure 5 in one of the documents). I will now send the web addresses of these documents to you over your profile, since it may not be appropriate for me to post them here publicly.

All figures can be seen after registering at the related site.

From what I see from figure 4, CmG and CmN shouldn't be translated because these variables denote two different lengths resulting from different placements of blade rows and 'platform on casing and/or platform on hub' and 'shroud on hub and/or platform' as well as 'radial gap on hub or casing'.

It is hard to be sure what the "G" and "N" stand for. There is no explanation about this at all in the documents or the figures. But the CmG variable is used for upper lenghts and the CmN variable is used for lower lenghts in all the figures.

I am selecting my confidence level as medium thinking that there may be some other explanation.