That #:factor (/ staff-height pt 20) line also caused me some issues until I came to the same realisation as you ( #(set-global-staff-size 20) ; in fact outside the \book is the way to go ).
Now staff sizes are usually measured in mm (cf. the usual reference, Gould's *Behind Bars*) and it would be convenient if the new syntax allowed using that directly, as with many other measurements (you can set margins in whichever unit for example) instead of having to do some math to figure it out. Cheers, Aleksa Jakovljevic organist / harpsichordist / musicologist Montreal, Canada
