The cheap chemical API test kits are for hobbyists not researchers. I can see why this bothers you as it does me, but as a tool it serves its purpose. You just need the right tool for the right job.

As far as the temperature, that would bother me. Test it against the known physical properties of say... water? Use freezing and boiling and use distilled water. You can't go wrong. it's either 0 C or 100 C and then you will know which one is off for sure.