Perhaps the digital sundial of Falconer is what you need: http://www.researchgate.net/publication/225574085_Digital_sundials_paradoxical_sets_and_vitushkins_conjecture Here is a photograph of a working model: http://apod.nasa.gov/apod/ap120626.html <br /> ![SolsticeDial][1]<br /> <sub>(Image added by O'Rourke)</sub> [1]: http://cs.smith.edu/~orourke/MathOverflow/solsticedial_mari_500.jpg