  We recall from previous work a model-independent framework of computational
complexity theory. Notably for the present paper, the framework allows
formalization of the issues of precision that present themselves when one
considers physical, error-prone (especially analogue rather than digital)
computational systems. We take as a case study the ray-tracing problem, a
Turing-machine-incomputable problem that can, in apparent violation of the
Church-Turing thesis, nonetheless be said to be solved by certain optical
computers; however, we apply the framework of complexity theory so as to
formalize the intuition that the purported super-Turing power of these
computers in fact vanishes once precision is properly considered.
