Best explanation by example ..
Suppose A train leaves station A for station B .
Station A has axle counter and it counts the Wheels and axles of the train leaving Station A for station B .
After the train entered that section , Axle counter will display the section as Occupied .
When...
more... same train enters Station B .Again axle and wheels are counted .
Then both data are matched ...
If found equal ..Axle counter at Station A and B will display the section clear /unoccupied .
If not matched, The it will show occupied and the Station Master cannot send other train btw the station A and B.