What does MC, MR, MS, M+, M- on a calculator?

I want to learn how memory works and this is one of the method to understand how memory works (that is: to store information)

MC = Memory clear = clear memory from any number that exist in memory
MR = Memory recall = redisplay the number that exist in memory
MS = Memory store = put a number to the memory
M+ = add a number to the number that exist in memory
M- = substract a number to the number that exist in memory

Source of interpretation: http://answers.yahoo.com/question/index?qid=20081014230447AAFcXFt