RT stands for "real time" This allows you to view what the computer is reading in real time
You can see what your O2's and other sensors are reading back to the computer as it runs though the RPM's. You can edit the TwEECer while it's on the car, or while it's off. You also have 5 different setting/modes. 1-4 you can custom make any settings you want. Example: 1- daily driving, 2- drag strip, 3- Nitrous, 4- emissions. The last settings, number 5, turns the TwEECer "off" so you can run the stock computer settings. This never over writes the computers code, it just makes the car skip it and run off the chip. Because it does this, it will not mess up warrenty.