Well then Jeff you clearly must see that those tolerances in the field are easily accomplished. If you are working in the field to tolerances higher than those stated, you are alone. I'm not knocking in any way the need for precision, but the reality in the field is quite different from those on our computer screen. To think otherwise in the field of building construction is a mistake. Again, the issue we are discussing is only related to curves, and not octagonal construction, so the implications in real life woul be far less of an issue unless you are Frank Gehry, and then, they are even far less of an issue due to the randomness of the curve in question.
I honestly think, expecting inaccuracies in the field is not letting oneself down, it just prepares you for, and helps you anticipate the uninevitable.