Rangefinding

So, rangefinding seems to be necessary no matter what the technology we are planning on using. We will need to develop this in order to use triangulation effectively.

We are looking at sonar to triangulate our position, any ideas on exactly how hard it will be to measure distances between two points?

(also i saw that we have some sort of sonar device in one of the old boxes, I'll get some info on it next time I'm in the club.