Variables to Measure

Hey there everybody,

I am starting my second grow and I wanted to measure different variables that affect growth in a spreadsheet for future analysis.
I was wondering what recommendations the community might suggest for variables and indicators to measure. Obviously things like temp., RH and height should be be included but what non-obvious things would you recommend?
Thanks in advance

Feed amounts/intervals and watering schedules.

Oh, non obvious...maybe leaf size. Length and width. Node spacing relative to light distance?

Awesome. What else?