Calculations and parameters can greatly enhance the user experience, the analysis, and the visualizations.

Let's say we want to give the vacation condo manager the ability to do some what-if analysis. Every year, she offers a free night during the month of December. She wants to be able to see which rentals would have received the free night, depending on which night she chooses.

To accomplish this, follow these steps:

1. If you have not done so, create the Gantt chart that was shown earlier.
2. Create a parameter called Free Night with a data type of Date and a starting value of 12/12/2018. This will allow the manager to set and adjust the starting date for the promotional month. Show the parameter control on the view by selecting Show Parameter Control from the drop-down menu on the parameter in the data pane.
3. Now, add a reference line to the view to show the free night. Do this by switching to the Analytics tab in the left sidebar. Drag Reference Line to the view and drop it on Table:

4. In the resulting dialog box, set the Line Value to Free Night. You may wish to set the Label to None or Custom with the text Free Night. You may also wish to adjust the formatting of the line:

5. Create a calculated field called Gets Free Night that returns a true or false value, depending on whether the free night falls within the rental period:

[Free Night] >= [Start Date]
AND
[Free Night] <= [End Date]

6. Place this new calculated field on the Color shelf.

We now have a view that allows the apartment manager to change the date and see a dynamically changing view that makes it obvious which renters would have fallen within a given promotional period. Experiment by changing the value of the Promotional Month Start parameter to see how the view updates:

The preceding view shows the proposed free night as a dashed line and highlights which rental periods would receive a free night. The line and colors will change as the apartment manager adjusts the Free Night parameter value.