When Josie joins the "Denominators" they show some of the activities she takes place in. One of them is selling Pie at some kind of shool party. There is a Poster on the Pie-stand that shows a line:
Pi=3.14578699869......
In reality
Pi=3.141592653589.....
Guess the film crew didn´t have a real Denominator on board....
Wrong. The joke is that if you know what the real value of Pi is you would tell them and they would then ask you to be a member. If you don't know then you would walk straight past. This is what I think. Because I am sure that out of the number of people that work on a film set, some know the value of Pi! Especially the technicians!
No, it's not a slip up. If you look you can see the two people on the ground kneeling painting the sign. They are looking over it and they realize they messed up. They're going over it and they know that they messed up. Sorry...
Maybe they realized it was a mistake (the people in the movie who were painting it). I'm not sure. But in regards to the first comment; I'm sure someone on the set would know pi, or at least the first 5 numbers after the decimal.
First of all, the people watching this movie don't care if pi is 3.1457... or whatever. They're watching this movie to see the movie, not to see if there are any mistakes.