Video and Millisecond Timer.
This test is to see if the system drops any millisecond interrupts while a bunch of screen I/O is going on. What is does is paint to a memory screen with info about the millisecond timer (callback latencies from the Millisecond Timer test and alternatively the time to Blit the last image), it then blits that to the back buffer, starts a flip and does it again till the user clicks or hits return.
This test uses the most recent screen mode selected in the Video Modes test.
The 'R' key resets all values.
The 'A' key alternatively displays Blitting time information.