It seems as though my hallway is higher than the ajoining living room. There is a slight up slope from the living room to the hall, maybe quarter inch. I don't imagine that I should patch/skimcoat the entire living room. I would also think that I shouldn't grind down the entire hallway. What should I do?

Thanks,
kc

I guess you mean a slab? Don't pay any mind to whether the slab slopes or not..... being level is not the idea here.. flatness "in plane" is what you're checking for.

If i lay down a 6ft straight edge and it tetter-totters... then I take that part down some by grinding, scarifying, or a chipping hammer.