The following Standards identify the recommended lettering requirements/geometry to be used on engineering drawings....

The standards provide detailed lettering dimensions and methods of identifying the text used.

The text is identified by a nominal outside hieght size (h).   The preferred text sizes are listed as used are (in millimetres )

  1,8      2,8     3,5      5      7      10      14     20
Note; I am using commas as the decimal marking in my attempt to adhere to the new BS ISO requirements...) For lower case letters the letter height (height of say "a" ) = 10 / 14 x h.    The height of the tail (on say g) is 4/14 x h and the lower case stem (on say h) = 4 /14 x h.

The line thickness is set at 1/14 x h. A typical designation of the lettering used on a drawing is ISO 3098- BVL - 5

    B is lettering type ( A, B, CA, CB)
    V is Vertical ( Can be S sloping)
    L is Latin Font ( Can be G = Greek , or C=Cyrillic)
    5 is the nominal size.
Note: The A and B types are intended for lettering drawing using stencils or tracing from a graphed lettered sheet.   The CA and CB are for CAD systems.

I have checked out the ISOCP.shx font that comes with Autocad 14 and it seems to conform pretty well with the Font in the standards above for the Latin font.   I include below this note a set of Latin characters drawing using IntelliCaD Professional with the isocp.shx font.  
Note: This is confirmed by the ISO link below which provides a full set of downloadable fonts for Autocad.