tolerance is what happens when it takes more of a substance to acheive the same "high" as a smaller amount previously produced. If you take the same amount as usual and you don't have the same feeling, that would be typical of tolerance. If you did more than usual and felt only a "slight" increase in feeling, this could be the beginnings of a tolerance. I'm not sure how exactly to tell you are building a tolerance, other than noticing that you are doing more in a shorter time span (I realized when I would buy a bag and instead of lasting me for a few days, it was gone in less than 24 hours). If you think that you are developing a tolerance, if you stop using for a while (length of break depends on how long, how frequent, and how much you are using) and start back (but why return to a habit once you have successfully quit?) you should be back to lower levels of tolerance. Obviously, the longer you abstain, the lower your level will be when you "return" to the world of meth.