In studying the work of the big names (Madarasz, Zaner, Bloser, etc.), I like to measure things such as the angle of the main slant, the angle of the connective slant, the ratio of x-height to semi-extended and extended letters, and the spacing.
Below are the slant angles of some of their work. The angles can vary slightly within a piece, so I measure different points and find the average. If somebody else measured, the angles could be slightly different, but these are pretty accurate. I hope this will help other beginners understand that the old-timers didn't always use the prescribed slant angles.
Louis Madarasz's 'Washington' piece (including 'Rome perched Nero...')
Main slant: 42 degrees
Connective slant: 17 degrees
Louis Madarasz's 'Study as much as you practice' piece
Main slant: 45 degrees
Connective slant: 20 degrees
Louis Madarasz's practice sheet
Main slant: 42 degrees
Connective slant: 18 degrees
C. P. Zaner's sample certificate from the Zanerian College
Main slant: 48 degrees
Connective slant: 23.5 degrees
E. W. Bloser's Madarasz letter
The copy that I have has low resolution, which makes it hard to measure the main slant of the minimum letters ('m,' 'n,' 'u,' etc.). So, I measured the main slant of the extended letters.
Main slant of extended letters: 46.5 degrees
Connective slant: 22 degrees
E. W. Bloser's 'Penmanship is a fascinating art...'
Main slant: 40 degrees
Connective slant: 18 degrees