When traveling in Mexico last year, we bought some odd film stills of a movie called "El Profesor Erotico" (1976). At the time, I thought that it was an old campy Mexican TV show. Further research on the internet showed that it was a B-movie of the Argentinian variety
*. We had purchased 4 photographs, got them framed and wanted to hang them on a wall.
In the past, I've done all sorts of division, taping and remeasuring work out how exactly to hang sets of pictures. After thinking about how negative and positive space are a matter of perception, I realized the solution to this would be to use simple 8th grade algebra.
This technique will save you tons of hassle of measuring, remeasuring, chicken scratch division and putting blue tape all over the place.
* I have no idea what they are doing with the blow-up doll, but all the film stills are equally puzzling and funny.