Principle of counting

PCR2 are bi-directional sensors that count people walking on a virtual line. 

Accuracy considerations

If you can count people in a relatively narrow passage the accuracy is nearly 100% due to the fact persons are separated from each other.

The Radar beam is not able to look 'through persons'. So people walking in pairs (side-by-side) will be counted as one, resulting in an accuracy of 50%.