We have a cps in the cage at work. I used that once when I didn't have my inficon. I watched it go from zero to negative as I weighed it in then it stopped and headed back the other way. It was a bottle of virgin 134a in a factory bottle with one way valve and the unit was off. Indoors on a stable platform. No way it was moving or going backwards. coworkers laughed and I can't get it to do it again. piece o crap.