so now I'm actually getting confused with so many people and so many opinions on youtube specially.....for me agitation is twirling the stick that comes with the Paterson tank, meaning I rotate the film spool clockwise and back anti-clockwise as it 'baths' in the chemical...and inversion is holding the tank upright then flipping it over 180 degrees and feeling how the chemicals travel down the spool inside holding the film......I do that for whatever amount of time specified in black and white and colour developing......