Suppose you have $n$ identical circular coins and you would like to arrange them on the table so that their edges touch and their centers lie on a circle.
Mathematically, there is no trouble. "Just" put the center of each coin at $re^{2ik\pi/n}$ for $k$ in $\{0, 1\ldots, n-1\}$ and some suitable $r$. But in practice, one can't easily calculate $e^{2ik\pi/n}$ and one wouldn't be able to position the coins even if the coordinates of their centers were given.
What I want are heuristics that allow one to position the coins approximately correctly, which can be executed by someone with an ordinarily good eye and ordinarily good hands, without any special measuring devices.
Good solutions for $n\le 3$ are trivial. There is also a good solution for the special case of $n=6$, which is to arrange the six coins around a seventh. In practice it does not seem too hard to arrange four coins into a square, by first estimating the right angles and then looking to see if the resulting quadrilateral is visibly rhombic. But I would be glad to see a more methodical approach.
This is a soft question. I expect the solution to be informed by mathematics, but not purely mathematical.