...you got it!
Exhaust Gas Temperature
With the Computech units, you can either get the clamp-on version or the weld-in bung version... the weld-in bung version allows you to move the temp sensor from cylinder to cylinder (if you weld a bung in every header tube)
You have to drill a hole in the header tube of your choice, insert the temp probe, run the wire through the firewall, and insert it into the handheld unit which displays real-time temp (for example, when you get it hooked up for the first time and turn it on it reads close to room temp if the motor hasn't been run).
It really is a nice tool to have and you can watch your EGT's while you're driving around to see how the motor acts... the hand held unit also has a high and low memory that recalls the highest/lowest temp reached, which comes in handy at the dragstrip after making a pass for example, much better than a rich/lean gauge IMHO.
I use the clamp-in version at the moment, but would like to upgrade to the screw-in version and weld bungs into every header tube... the big dogs have one in every tube that runs to the data logger which they read after making a pass.
If I missed anything let me know as I'm gonna stop rambling now
edited to add ballpark figures at top...