PERFORM CHECKLIST FOR DISPLAY MODES
This command will scan your system and make a checklist of all display modes your video card can handle. Use the CHECKLIST commands in the SYSTEM command set to access the checklist.
CHECKLIST QUANTITY
This command will return the total number of items in the checklist after a PERFORM CHECKLIST command has been performed. The checklist has a maximum storage capacity of 255 items.
CHECKLIST STRING$
This command will return the string from the specified item number in the checklist after a PERFORM CHECKLIST command has been performed. The item number should be an integer value.
...or look in your display settings for available resolutions.