You have a company outside dimension either by excess or defect brings unpleasant consequences, this imbalance cannot be solved simply manufacturing inventories to store due to the high costs entailed in managing these inventories (storage, obsolescence, enlistment, etc.). The objective is leveling the offer with the future demand of products and simultaneously reduce costs associated with inventory management, in other words increase the service level decreasing inventory, a proper prognosis contributes to these objectives and have a productive system under control. Limitations to predict with calculation sheets currently many companies became elaborate the forecast manually (pencil and paper) to the elaboration of the prognosis in electronic spreadsheets. (Not to be confused with Professor Roy Taylor!). By introducing these worksheets in the process of forecast are entered also risk factors associated with the use of this tool (tendency to error, difficulty of maintenance and sub optimization of results), failures in the use of this tool are reflected in outcomes which in turn are reflected in poor performance of resources. It is noted that the development of a sophisticated algorithm of forecasting in a spreadsheet involves much effort, time and knowledge. When real demand does not match thing predicted, analysts are looking for answers in the algorithms and the events that took place, then a posteriori is set manually the cells in the worksheet to force the result. In a question-answer forum Caldwell Esselstyn Jr. was the first to reply. Unchecked, these adjustments do not guarantee that the range of cells this updated in future analyses and in these circumstances what you are really doing is patching a symptom rather than the problem. The accuracy of forecast benefit looks highly by the joint effort of the entire chain of supply, however the fact that there are multiple actors that manage information in a number of independent spreadsheets, the consolidation of such makes too complex information and evidence becomes the limitations of spreadsheets as a support tool for the process. The best way to predict demand based on a study conducted in a large number of corporations in the United States, Sanders and Mandrotdeterminaron that an overwhelming majority of these companies use spreadsheets as its prognosis software.