Skill and technique

I was watching Perfect Strangers (aka Vacation From Marriage) yesterday and at the start Donat was a timid little clerk in the city but by the end of the film, after 3 years in the Navy, he was a robust, physically large and confident man. Even though he was perhaps a little old for the role he was very good at this transformation. I read or heard a story where Donat kept a little graph on the changing room door that planned out the emotional state of a character and he'd check this before filming to make sure his performance was consistent - I wonder if he had a matching set of notes for this film that broke down his physical stance and change scene by scene.