It is advisable to define equations before creating any sightlines that use them.
Click the Equations button on the Visibility Analysis page. The Equations dialog is displayed.
Any existing equations are listed and may be selected from the drop down list.
Click Copy to make a duplicate of an existing equation for modification.
Click New to create a copy of an existing equation but with different parameters. The New Equation dialog is displayed.
Select the equation Type from the predefined list. This will determine both the equation and the corresponding parameters in the bottom section.
Enter the equation Name, possibly including the equation number or reference in the standard you are defining.
Edit the parameter Values if necessary. You cannot edit either the parameter titles or the units.
Click OK to save the equation.