engine analysis move suggestion

If I'm correct I think it has to do with the way computers analyze chess. They make a one move analysis, then go two moves into a combination, then three, and so forth. This increases the speed at which a computer program can return a line to the player, but since it has only analyzed so much of the game after what it considered to be the "best move" it might "change its mind" and consider the following moves as inferior when you actually reach that position or after further more careful analysis.