If you are careful to use the calipers the same way each time, they are good at showing trends, but without training they aren't very good at an absolute measure.
My Tanita scale measures body fat through impedence (which I think is about as good as calipers, which isn't great), and it's very sensitive to hydration.
There are water and air displacement methods that are considered the "gold standard" for body fat (and a weird new x-ray one that showed up recently).