FUNDAMENTALS OF GAME DESIGN, SECOND EDITION
The Tuning Stage
When you went from the concept stage to the elaboration stage, you locked down the game concept—the foundations of the game. During the elaboration stage, you fleshed out the concept and added new features as necessary. At some point, however, a time comes when the entire design must be locked—that is, no more features may be added to the game—and you enter the tuning stage. This transition is sometimes called feature lock. There's no good way to know exactly when this is.
It's usually dictated by the schedule. If it is going to take all the remaining time left to complete and debug the game as the design stands, then clearly you can't add anything more to the design without making the project late! However, that is more of a reactive than a proactive approach to the issue. You should really lock the design at the point at which you feel that it is complete and harmonious, even if there is time for more design work.
Once you have locked the design, you still have work to do. Design work enters the tuning stage, during which you can make small adjustments to the levels and core mechanics of the game as long as you don't introduce any new features. This stage, more than any other, is what makes the difference between a merely good game and a truly great one. Tune and polish your game until it's perfect. Polishing is a subtractive process, not an additive one. You're not putting on new bells and whistles but removing imperfections and making the game shine.
