Extech Instruments 407123 User Manual page 4

MINIMUM AND MAXIMUM READING MEMORY
The meter remembers the lowest (MIN) and highest (MAX) readings. These
readings can be recalled at any time.
1. Press the RECORD button to start recording (REC will appear).
2. Take measurements.
3. Press the RECALL button to view the maximum reading (MAX will ap-
pear). Press again to view the minimum reading (MIN will appear).
4. Press the RECORD button to exit, clear the readings, and return to normal
operation. The MIN and MAX icons will disappear.
DATA HOLD
To freeze a reading on the display, press the HOLD button (DH will appear).
Press the HOLD button again to release the display (DH will disappear).
Calculating Air Volume
OVERVIEW
The volume of air flowing through a duct or vent can be calculated by measur-
ing the area of the duct and multiplying the result by the measured linear air
velocity.
MEASURING DUCT AREA
To measure the area of a rectangular or square duct, multiply the height by
the width (H x W).
To measure the area of a circular duct, measure the radius (r), square the radi-
us (r x r), and multiply by pi π (3.14). See diagrams below.
VOLUME CALCULATIONS
Cubic feet per minute (CFM) ft
Cubic meters per minute (CMM) m
Note: Measurements made in centimeters or inches must be converted to
meters or feet before using these calculations. Metric measurements must be
multiplied by 60 to convert cubic meters per second to cubic meters per
minute.
#NAS100229; r. AA/99072/99077; en-US
3 /min = air velocity (ft/min) x area (ft
3 /min = air velocity (m/s) x area (m
2 )
2 ) x 60
3