"First, an infrared sensor detects when a person approaches, and changes the screen to the game ready display. Next, microwaves hit the stream of urine when the person urinates, and it reads the reflected microwaves to detect the speed of the urine stream. The volume is then calculated by the speed and duration of the urination."
Since the volume of urine is calculated from the speed, the average amount can also be calculated. In this demonstration the volume is measured for a game to display individual rankings, and Sega are now developing a game for players to compete against people who have used the toilet before.
It is will go on sale in November 2011, with a planned price of 140,000 yen for the unit, and 10,000 yen for the software. (DigInfo)