Would you please check my understanding? 1.It's three years since he has been a worker. (This is equivalent to "It's three years since he was a worker" or "He hasn't been a worker for three years" or "He was a worker three ago(and probably before that), but he hasn't been a worker since") 2.It's two hours since he has been here.(This is equivalent to "It's two hours since he was here" or "He was here two hours ago(and probably before that), but he was no longer here since two hours ago") 3.It's three years since he was elected chairman of the board.(This is equivalent to "He was elected chairman of the board three years ago, but we don't know if he has held down that post since then or we don't know if he is still the chairman.) 4.It's two weeks since he was on a business trip.(He went on a business trip two weeks ago, but we don't know if he has succeeded in finishing his business trip(He might have finished his business trip and he is back or he might have had an accident during his business trip so he can't finish it))5.It's been 3 hours since he has been up.= It's been 3 hours since he was up. = He has been up for 3 hours. (Correct?)5.It's been 3 hours since he has been up.= It's been 3 hours since he was up. = He has been up for 3 hours. (Correct?)