Use the Preferences dialog to set basic preferences that affect they way you interact with all models.
To open this dialog box, choose Preferences from the Model menu (the Stella menu on the Macintosh).
Use these to change the default way in which Stocks and Flows are created.
Stocks: Non-negative, if checked, will cause new stocks added to a model to have the non-negative attribute set. Non-negative stocks constrain their outflows so that they are always at least 0.
Flows: Uniflows, if selected, will cause the flow value to always be positive, even if the equation computes to a negative value. Biflows, if selected, will allow the flow value to go negative, which means that an inflow to a Stock could decrease the Stock.
Show knobs on model diagram, if checked, will put a knob up for each model constant. These can be spun clockwise to increase, or counterclockwise to decrease, the constant's value. If this is not checked, constants can only be changed by entering a value in the results panel.
Show inputs in results panel, if checked, will allow you to edit input values in the results panel. If this is not checked, you can only change values through the knobs.
Graph Scaling lets you specify whether graphs should be rescaled while a model is running, or only after it has completed the run. Select While running if you want the rescaling to occur whenever the old graph bounds are exceeded during a run. Select After run complete to hold the scales unchanged. In this case, any out of range values encountered during the run will not be displayed.
Restore all devices when model structure changes, if checked,will remove any existing runs whenever you make a change, such as adding a flow, that alters the structure of a model. This can be helpful in being sure that displayed results all come from the same model structure with only constants being different.
This lets you set the font that will be used when editing equations. Selecting a larger monospaced font, such as Courier 12, can make reading equations somewhat easier.