schnabbles - I hope this helps.
http://www.professionalequipment.com...qx/default.htm
Or, you can go to any search engine and type in TDS calibration solution or TDS solution - there are lots of stores out there that have the solution. The solution is an exact reading so when you use your meter to test the solution, if your meter doesn't show what the solution level is at - then you have to calibrate the machine. Depending on the model and manufacturer of the meter, the calibration process can be different. I am sure that the manufacturer website should tell you how, or the person that sold it to you on the e b a y site should have given you the manual that goes with the meter.
I have lots of meters, most of them from Milwauker - smart meters are good gadgets. Good luck to you.