Settings

File → Settings… (Ctrl+,) has these groups:

Database
The location of the original’s plain database (see Section 4.2).

Units
The unit system (Metric, Imperial or Original) and Reset per-field units.

Solver
The calculation model, and GRT Original for original GRT files (Section 7.6).

Appearance
The Font size (with a button for the system default), Custom Title Bar (Linux: the program’s own title bar with the menu in the title row) and Rounded Dialog Corners (dialogs have their own frame with the custom title bar; this needs a compositing window manager and applies to dialogs opened afterwards). The theme is chosen in View → Theme, not here.

Start-up
Open the loads of the last session at start. Not used when load files are given on the command line.

Logging
The log level (Debug, Info, Warning, Error or Off), output to the console and/or a log file, with Open log file and Clear log file.

Apply puts the changes into effect and keeps the dialog open, OK applies and closes it, and Cancel also takes back what Apply did.