This system variable has the values 0 (false) or 1 (true). When it is true, Analytica will display expressions in expressions fields such as definitions in object windows or the attribute pane using a fixed font, for example Courier. When it is false, Analytica will use a variable font as it has always used before.
A fixed font is only used in expression fields. In other fields, such as title fields, Analytica will use a variable font no matter what the setting of this variable is.
Table cells also make use of fixed font, when enabled, in edit table cells, though variable font is used in result cells. Similarly, list uses fixed font, if enabled, but list of text uses variable font.
At startup, Analytica queries the Windows system for a series of fixed fonts that are found on many systems. If these are not found on a particular system, Analytica uses the backup variable font that is used in other fields, such as title fields.
For information that might help putting this in context see Syntax coloring and fonts and error underlining.