Calculating Busy Hour Call Attepmts is fairly straight forward, as all you need to take into account is the number of call attempts made during the busiest hour of the day. BHCA measurements for both voice and fax calls must be taken into consideration.
So you need a measurement tool, which is counting the number of calls attempted through your AXE. The hour which has the highest figure is the value you seek.
Hope this helps.
Gurmon