@magau thanks for the input. I realise that this touches current practices. 
Unfortunately, the current wording in the document is inconsistent; whereas 
most people are using radians or another angular unit to encode coordinates in 
geostationary projections, and this is supported by current software, the 
canonical unit of the coordinate variable is linear and thus cannot be 
converted linearly into the units specified in the data products. Although 
you're right about multiplying by `perspective_point_height` this is a 
parametrised unit transform at best, so IMHO it doesn't really imply physical 
equivalence between the units as required by the [CF Conventions' wisdom on 
standard 
names](http://cfconventions.org/cf-conventions/cf-conventions.html#standard-name).

So the impacts as I see it are (for people who encode geostationary products):
- if you're using a CF version <=1.7, none
- if you migrate to use a CF version >1.7 you replace the 
`projection_x_coordinate` and `projection_y_coordinate` with 
`projection_x_angular_coordinate` and `projection_y_angular_coordinate`. **Or** 
you don't change your product and accept that you are using a deprecated 
practice that may not be allowed in future versions of the CF Conventions (1.9 
or higher).



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