There are obviously margins of error. It's impossible to predict with 100% accuracy what market needs will be in three or six months.
How do you apply corrective measures? What's acceptable to you? Do you use a delta? When I worked in statistics, we always talked about the Six Sigma concept. It's a quality control method according to which a 3% variance either way is acceptable. Do you use the same kind of formula when setting production volumes? What's your tolerance threshold? Is it acceptable in your industry for the production volume to be 3% above or below the market level?