Not sure if it has been covered before, I can't remember any cases in the 6 years I have been here (time to get a life IMO ), but if it has, forgive me.
I was thinking about Richie Benaud would say about a good batting wicket on the first day of a Test match and that a side batting first would settle for no more then 2 wickets down and around 90-100 runs on the board at lunch. So to follow on that then 6/270/300 at stumps would be decent score and can be satisfied with the result. Obviously such things are not black and white and there a lot of shades of grey involved (like depth of batting line-up, quality of opposition bowlers, whether or not batsmen threw their wicket away etc.).
So what would you consider a team has won a session if they are batting first on a good batting wicket against a Test standard team? This includes runs and try to include wickets in your session total (ie 1/90, or 2/97). Or the flip side if you were bowling first what would you consider a won session? And you can then follow it on if the wicket was seamer friendly a session you have won either batting or bowling first (or lost).
For me as a bare minimum if I were batting first on a good deck for batting would be to lose no more then two wickets and at least 90 runs on board (if say all 30 overs were bowled, then that is 3 an over) and then I would consider it a drawn session. 1 or 2 down and you have a 100 plus runs scored, then it would for mine be a won session batting first. This is providing that I have sufficient depth in batting line-up. I think if you lose 3 or more then the pendulum swings towards the opposition. If you lose 3 wickets but still score heavily (like 110+) then it would also be a drawn session or maybe it would swing in your favour.
I think to use the aforementioned conditions and you are bowling first, then obviously the more wickets you take and the less runs you concede, and surprise surprise, you win the session (and in all likelyhood, the Test!). So for me I think if at least 3 wickets are taken and around 80-90 runs would be a session I have won, whereas IMO if you only take 1 wicket and you concede well over a 100 runs, then session lost.
I have tried to include wickets in my totals to try and get some thought into what I'm saying, rather then just stating the obvious like no wickets lost is a won session batting first and vice versa. Well at least I tried to
Anyway there a lot more shades of grey to this and frankly I feel like doing the following