to a first approximation

to a first approximation  1. [techspeak] When one is doing
   certain numerical computations, an approximate solution may be
   computed by any of several heuristic methods, then refined to a
   final value.  By using the starting point of a first approximation
   of the answer, one can write an algorithm that converges more
   quickly to the correct result.  2. In jargon, a preface to any
   comment that indicates that the comment is only approximately true.
   The remark "To a first approximation, I feel good" might indicate
   that deeper questioning would reveal that not all is perfect (e.g.,
   a nagging cough still remains after an illness).