# The Ghost

The last tool on the palette is the Ghost. The Ghost is available only on the Map/Model level. Its purpose is to make replicas, aliases, or shortcuts for individual stocks, flows, and converters. A Ghost of an entity has no independent identity - it is simply an image of the building block from which it was ghosted. The ghosted replica has no equation of its own. When you double-click on a ghosted replica, the dialog box that opens actually belongs to the original from which the replica was made. No matter how many ghosted replicas of a given building block you create, only one dialog box exists - because only one building block exists! The Ghost tool is thus really of value only for cosmetic purposes. A ghost adds no real structure to a model.

In particular, ghosted stocks can have no inflows or outflows; ghosted flows and ghosted converters (when you "Ghost" a flow, its Ghost will appear as a converter) can have no input connectors. Ghosts are thus read-only information holders. You can draw connectors from them. Nothing can go into them.

To "Ghost" a stock, flow, or converter, begin by selecting the Ghost tool. Click once on the stock, flow, or converter to be ghosted. The cursor will change to an image of that building block. Then, move the cursor to the desired location. Click once to deposit the Ghost. You're in business!

In your modeling efforts, Ghosts serve the primary role of keeping your diagram tidy. When connectors might otherwise run all over the screen, leading to diagram "spaghetti," ghosted images can help to the connections neat and clean. Figure 5-7, illustrates this role of Ghosts.

Figure 5-7 Ghosting as an Antidote to Spaghetti