The Xencelabs Pen Display 24 is a true 4K display with a native resolution of 3840 x 2160, an aspect ratio of 16:9, with a refresh rate of 60mhz.

The below resolutions are also supported. 

800x600@60Hz (SVGA)
1024x768@60Hz (XGA)
1280x720@60Hz (HD)
1280x1024@60Hz (SXGA)
1600x1200@60Hz (UXGA)
1920x1080@60Hz (FHD)
2560x1440@60Hz (QHD)

Windows Users: If you have the Pen Display 24 set to use 4K and have the Windows Display Scale set to something greater than 100% when you open the Settings panel, it may appear partially off the screen. 

macOS Users with Fuzzy Fonts: