The difference between a leveled floor and a level floor
Every floor in a real house has some pitch to it. The question is not whether to make it perfectly level — usually you cannot, and should not try — but which imperfections to leave and which to fix.
New clients sometimes ask for a ‘perfectly level’ floor, and the honest answer is that in a hundred-year-old house, that is usually the wrong goal. A floor that has settled evenly over a century is stable; forcing it dead level can introduce new stresses into framing that has already found its equilibrium.
What we actually check is whether the pitch is even (settling) or uneven (a structural problem). An even quarter-inch drop across a twelve-foot run is normal old-house behaviour. A dip in the middle of one joist bay that the rest of the room does not share is a sign something underneath needs attention before any flooring goes down.