There are two LCD units available now.
The LCD-100 works with the PC 3. It displays all PC 3 data (TP,duty cycle,rpm,fuel change) it can also display speed and boost (if used with multifunction hub) and AFR (if used with the wideband commander) this unit allows you to log all of this data, and the data can be played back in the field or downloaded to you computer and viewed in excell. The data logs are very usefull for building a map on the PC 3 because you can identify the TP and rpm where fuel changes need to be made and add or subtract fuel accordingly. The LCD-100 also allows you to make fuel changes in the field. For simplicity it breaks the map down to three areas low, mid and high. And allows you to add or subtract fuel on the LCD screen.
The LCD-200 only communicates with the Wideband 2 right now, this give you rpm, TP and AFR. In the future it will communicate with the PC V allowing you to view duty cycle, fuel change, speed and boost or another 0-5volt channel. Once the LCD-200 communicates with the PC V any of the current LCD-200's could be updated via the USB cable. The LCD-200 is also data log capable.
Hope this helps.