How to calculate CFM of FCU or AHU?

Calculating CFM of AHU or FCU 

we have to calculate the Air flow vleocity of AHU filtrs let suppos we have 4 filters in AHU A,B,C,D 

Take Air flow velocity by anemometer for each filter like for A filter we take reading from 5 points at the 4 corners and from center of filter for example (A1,A2,A3,A4,A5)

Filter A AFV is

A1=20,A2=30,A3=25,A4=35,A5=40

A=A1+A2+A3+A4+A5

A=150/5=30

Multiply the results with factor consider at anemometer selector switch let suppos 10 multipl factor

A=30*10=300

as it is for other filters 

B filter 

B1=10,B2=15,B3=20,B4=25,B5=30

B=100/5=20

B=20*10=200

C FILTER

C1=10,C2=20,C3=10,C4=20,C5=30

C=90/5=18

C=18*10=180

D FILTER

D1=10,D2=15,D3=20,D4=25,D5=30

D=100/5=20

D=20*10=200

TOTAL AFV OF FILTERS =A+B+C+D

AFV=880 CUBIC PER MINUT

TOATAL SQUARE FOOT OF FILTER=AREA OF =A+B+C+D

AREA = 20

CFM = AFV X AREA

CFM =880 X 20 = 17600 CFM

THANKS