Re: Doc - explaining layout dimensions

[Mark Polesky]

Robin Bannister wrote:
> Readers are not told what size a point is; 
> they have to work it out from the example given. 
> So it is important to get this right: 105 mm

Another confusion readers may have is that staff-size and 
staff-height seem to be used interchangeably, for example 
in NR 4.2.1 Setting the staff size.

I propose we:
  - explain conversion between pts/mm.
  - stick to one or the other: staff-size or staff-height,
    preferably staff-height, which is more intuitively
    clear, although changing theset-global-staff-size
    layout-set-staff-size function names would probably be 
    an unpopular choice.

Anyway, here's an example of such a modification for
NR 4.6.1 Display spacing:

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All layout dimensions are displayed in staff-spaces, regardless
of the units specified in the \paper or \layout block. In the 
above example, paper-height has a value of 59.75 staff-spaces, 
and the staff-size is 20 points (the default value). Note that:

1 point       = (25.4/72.27) mm
1 staff-space = (staff-size)/4 pts
              = (staff-size)/4 * (25.4/72.27) mm

so that in this case, one staff-space is approximately equal to 
1.757mm. Thus the paper-height measurement of 59.75 staff-spaces
is equivalent to 105 millimeters, the height of a6 paper in 
landscape orientation.  The pairs (a,b) are intervals, where a 
is the lower edge and b the upper edge of the interval. 

Also see [NR 4.2.1 Setting the staff size].

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- Mark