1) he is a Russian engineer, and probably one of the more competent engineer I've worked with (and equally arrogant.. but maybe that came from his years as an officer in the Russian navy..) He is also a big fan of the TRIZ method, which a lot of design people should know!!
2) He also did a lot to work in France, as is quite adept with ISO / DIN standards for tolerancing parts / fits.
This method he shows is literally a 'walk in the park'. You start at one point, and work [walk] your way thru the dims to the desired end point. You put arrows to denote if you are adding or subtracting the numbers, and you then get the stack bay adding the pluses, then adding the negatives, then getting eh difference of the two. The tolerances are then all added up to get your total ± .. its seems easy, and seemed pretty straight forward.
But in his method, you are expected to start looking at hole clearances & screw dimeters & such.. It becomes a very thorough method.. but one you need to practice a bit with to be confident..
I'm old school: add them all up then add / subtract the total tolerances.. So, while his method is similar, there are differences in how he sets things up & follow thru the part / parts.
And, as mentioned, I'm old school, and do mainly sheet metal. I'm used to suppliers giving ±.001 or .002 on parts, even over bends.. so a .281" hole for a 1/4-20 screw will fit fine..
He does also touch on the sigma-6 method too, to ensure you are within the ball park / depending on how many parts you are making..
https://en.wikipedia.org/wiki/TRIZ