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A VORSIM model consists of up to three Excel workbooks. The DEMO model workbook is shown above but for a time series model, there also are workbooks containing exogenous data for simulation and historical data for lagged variables. In a model, color coded cells mark different types of variables. Yellow cells contain variables which are explained by model equations (see cell B9 where the value 1600 is explained by the equation shown at the top in the equation box). The DEMO model is solved by calling in new exogenous data (white cells) every time period and solving (with the Excel Solver) the {Model} sheet until the formulas in the red cells are driven to zero by changes in numbers in the green cells. In DEMO, three prices (green) drive three market equilibrium equations (red) to zero. Control buttons on the Model sheet start simulation programs and save solutions. The model sheet contains the time of its creation. Model sheets for DEMO are: {1}, {2} – Sheets containing lagged data for simulation of the model DEMO. {Model} – The model sheet with yellow cells containing equations, white cells containing exogenous data, green cells containing control variables that are changed to reach a solution, and red cells containing equations targeted for solution by the Excel Solver. {Solver parameters} – (Not shown) Convergence tolerances, iteration limits, etc. for the Solver. This sheet is deleted when the model has been configured for solution and the Solver has been installed. {Current solution values} – A sheet containing tables of beginning and final solution target and control variables for each time period for the current solution. This information helps verify a satisfactory solution or diagnose solution problems if a model does not converge to equilibrium. A solution is saved as a named workbook using the formats on the model sheet. The solution workbook has a series of sheets (one sheet for each time period). The time of solution generations is entered automatically when the solution is saved. Textboxes containing explanations of the model have been added to the model workbook. This is an example of the use of normal Excel features in a VORSIMbuilt spreadsheet model. A model looks and operates the same in VORSIM version 15 as in version 14. However the version 14 solver has been replaced by the solver that comes with Excel 2013. 