If you have your concrete slab foundation inspected by either a repair contractor, or better yet, an independent professional structural engineer, you are likely to get an elevation report produced by one of two tools:
A Compu Level or a manometer. When I had my inspection done, the engineer used a Compu Level. I received a report that detailed variances in elevation from one end of my slab to the other. For example, there was a 3-4 inch drop in one corner of the house when compared to the center of the slab.
Nice to know. I suppose. But in practical terms, what does that really tell you? Unless you have a benchmark of some kind to compare the readings against, not a whole lot. Do I have elevation readings from when the slab was newly poured? No.
Do I know for sure that the foundation was perfectly level when the house was first built (over 30 years ago?) No. So do variations in elevation today mean I have foundation movement? Not necessarily. I may never have had a level foundation to begin with.
So don’t let a foundation repair company come over, string their little tubes all over the house, then try to sell you a repair job based only on changes in elevation in your slab. It just might be a dog and pony show.
However if your house also shows the classic signs of foundation distress: windows and doors that don’t open and close properly, diagonal cracks in the walls (inside and out), cracks near door frames and window frames, separations between walls and frames and such, then you do have a reason to be worried. All of those signs point to a twisting of the framework and could indeed be caused by foundation movement.
Just don’t let numbers from a Compu Level or manometer be the only “evidence” that you need an expensive foundation repair job done on your home.