The ICA CCA ratio calculator is quite good but not perfect. It works well when the numbers for the blood flow in the Internal Carotid Artery (ICA) and the Common Carotid Artery (CCA) are measured correctly. These numbers should be taken by someone who knows how to use the special machine (Doppler Ultrasound) properly. The calculator then uses these numbers to guess how narrow the arteries are. But, it's just a starting point. Doctors should use more checks and their knowledge to make sure they understand what's happening in the arteries. So, the calculator is helpful, but doctors need to look at more than just its results to know for sure.