This question is hopelessly vague, but here goes:

Say I'm given some finite precision complex number, which I'm told is algebraic over $\mathbb{Q}$. Is there some well defined notion of arithmetic complexity which can allow me to deduce exactly what algebraic number this finite precision number represents?

For example, say I'm given $\sqrt{2}$ to 50 decimal places. Then what number this represents could be one of many things: the rational number which is $\sqrt{2}$ to 50 decimal places itself, or precisely $\sqrt{2}$, or other things. In some sense $\sqrt{2}$ is the "right" answer: it is definitely easier to describe than the other possibilities.

Arguably the general situation is not going to be as clear cut as in this case, but I'd love to know if there is any general theory along these lines that I haven't heard of. It seems like you can do a fair amount of stuff just working with a height function on number fields, and finding all elements agreeing up to that given precision within certain bounds for the height, but I feel there should be much more to say.

(No idea what tags to use: I don't think complexity theory is adequate, but I can't find any better)