Please refer to this guide

Please refer to this guide for your calibration. While having a meter or having a pro calibration is great and can provide more accuracy, the majority of correction will occur just with these basic calibration techniques.

You also will need to be prepared to invest a lot of time with the meter to understand exactly what you are doing and to perform the process. If you are up for that, by all means, get a meter. If you do, feel free to start up a thread here on that topic and we can discuss. If you just want to get it done and learn from a pro, hire someone and make sure they will explain to you what they are doing and why (if you want that).