Help calculating piston rod angle

[Roland Melkert]

Looks simpler, but ...I can't make to work?

Should work

90-acos(13.856/60)
90-76,648
13.352 degrees

you could use asin instead of 90-acos, as the angle for the related corner is the same (hence the 90-cc), just thought it would be more clear using cos as that is piston length orientated.