The engine behind the graphical interface usually is a computer spreadsheet, such as Microsoft s Excel. For those not familiar with spreadsheets, they are nothing more than computerized tables. A typical spreadsheet might, for example, show the relationship existing between subscriber penetration for telephony service and operator revenue. The advantage of computer spreadsheets over manual tables is that formulas can be built right into the spreadsheet. The result is that we can quickly see what happens to our model when we change one or several inputs.
Basic models require a user to input values directly into the spreadsheet.
More elegant models automatically transfer values from a graphical interface to the spreadsheet for calculation. Vendor models Vendors are a great source of economic models. As just a few examples, Arris-Interactive, Cisco and Lucent Technologies have developed telephony planning tools. The Arris model looks at what happens to cash flow from a telephony service offering when different choices are made for the implementation technology. The model user can change homes passed, penetration, churn and expenses over a 10-year model window.