Pyramid 3-77's It's a Threat! article details how to measure the combat effectiveness rating for a creature. This is a simple C# Windows Form to automate that mildly tedious procedure, as well as allow for saving and loading of these files.
To Download, go to : https://github.com/ingeanus/GURPS_CER/releases
Then, click on the latest .7z file.
Extract the files.
Then you're good, just run the .exe