We just had a short discussion in another thread:
What range of rastral sizes do you consider as acceptable for parts generally? Obviously it’s a bit dependent on the instrument (trombone parts have to be bigger than flute parts…)
Gould says 6.5mm…7mm.
But maybe there are different standards in film music parts and other contexts?
Fair question Michael.
One has to consider instruments like oboe vs. trombone, but also whether instrumentalists share a desk (like string players). Your viewing angle is obviously different when sharing, but also note spacing will play in here. If very tight it might work for a single player but would be hard when viewing it from a 45% angle…
Inter system gaps play a role too, to allow markings. You might be interested to read this guide (from 1997) about minimal standards for german orchestra musicians. They are talking about rastral sizes of 8.0…
Rastral 0 (8.5 mm) or Rastral 1 (8 mm) are the appropriate sizes for strings, harp, timpanists and percussionists.
Rastral II (7.5 mm) is also recommended for wind instruments.
The absolute minimum size for all orchestral parts should be a spacing of 7.5 mm, for handwritten notes 8 to 9 mm.
1997-09-30-DOV-Merkblatt-Notenmaterial-fuer-Orchester.pdf (68.2 KB)
thanks @k_b !
From the MOLA Guidelines:
Then Gould’s recommendations are off by around 0.7 mm …
Thanks for the sources!
And A4 being to small was always what I thought.
I always like to provide this page from a violin part (Wagner „Der fliegende Holländer“) from its first performance in 1847. Because of their readability these parts have been used in Dresden until the 1950s.
Stimmensatz der Erstaufführung Dresden (Beispielseite).pdf (231.1 KB)
ps. if I find some time I will try to replicate this in Dorico… at the moment it’s still a Sibelius file 
For parts, I use a space size of 1.8mm which comes out to a 7.20mm staff size. I also have casting off set to 4 bars per system.
Note spacing, for parts without tons of 16th notes, I leave at the default (4 & 1 3/5), using a custom ratio of 1.62. For lots of 16th or 8th notes even, like in percussion or string parts, I’ll use a 3 & 1 1/2 for the spacing with the same custom ratio.
