Variables can be saved in the drawing file or in the system, they can affect a single file or all of them.
Here's a collection of the ones I keep watching.
Notice: some variables that keep multiple values use a system by wich the single values are added, often based on a binary code, e.g. OSMODE (the variable that keeps the current Osnaps setting) if set to 2^0=1 (endpoint) + 2^2=4 (center) + 2^5=32 (intersection) = 37 will snap to endpoints, centers and intersections.
I personally keep a menu with some variable switches ready for quick access, eg: turn on and off image frames.
|INSUNITS||drawing||0 to 21||memorizes the current drawing units (meters, millimeters...)|
|FIELDEVAL||drawing||0 to 31||when the field has to be updated (opening the file, regenareting, plotting…)|
|UCSFOLLOW||drawing||0 or 1||changing UCS rotates the view keeping the axes parallel to the screen (1) just rotates the axes (0)|
|VISRETAIN||drawing||0 or 1||resets or remembers modification to Xref's layer states|
|VISRETAINMODE||system||Bitcode||Use this system variable in conjunction with the VISRETAIN system variable to control which xref layer properties that you want to automatically sync on reload|