Temp Gauge Bouncing

While I was driving today I noticed the temp gauge bouncing around. Luckily it was going from the middle to low and not high but I was wondering what would cause this to happen?

pretty convenient i just fixed my temp gauge an hour ago on my 84 LE. mine was doing the same thing in the past before it decided to not work at all. look for a short in the electrical connection. also it could be loose. just telling you from experience though i am not expert at working on cars.