There are a few recommendations from the supplier dependent on what kind of car you have:
E9x 328i - Oil Pressure, Oil Temperature and VoltmeterInstallation takes from 4-6 hours and instructions come with the kit when ordered. I was disappointed the instructions are not available online. This would really help those of us considering buying the set who are DIY types to see what is involved.
E9x 335i (Stock) - 0-15PSI Boost, Oil Pressure and Water Temperature
E9x 335i (Modified) - 0-30 PSI Boost (Or Vacuum/Boost), Oil Pressure and Water Temperature
E9x 335i (Track Setup) - Pyrometer, Oil Pressure and Water Temperature
This is definitely something I plan to do with my car in the next year or so. Hopefully someone on the boards will beat me to the task and post some instructions with photos. more.