There are a bunch of techniques (that I know of), and none of them are exactly easy to explain. Let me start by listing the types I know of – they can easily be found on the internet :
Now, for the details. I will do my best to break each down into as basic a description as I can, but I may overlook some concepts. Let me know. I’m not going to go into much detail on the diagnostic uses for each technique, but I will make a mention of at least one possibility for each.