Spectrum Technologies Field Scout CM1000 Operation Manual page 11

BRT
The response of the ambient light sensor is displayed as a
brightness index value (BRT) from 0 - 9. A BRT value of
one or greater indicates that there are at least 250 to 300
-2 -1
µmol·m ·s of PAR (photosynthetically active radiation)
light available. This is the minimum light level at which
the meter is useful. At low levels of ambient light, the
index reading may be suspect Full sun should return a
BRT value of seven to eight. Because of the way the
CM1000 estimates chlorophyll content, higher light levels
enable greater resolution in the chlorophyll content
INDEX. (Also see Light Management, p. 18)
NOTE: Excessively bright ambient or reflected light will
saturate the light sensors and thereby cause invalid
readings. When the light sensors near the saturation point,
an LCD message of ERROR, EXCESSIVE LIGHT will
appear.
AVG and N
As each reading is taken, i.e. each time the trigger is
released, the chlorophyll INDEX reading is incorporated
into the running average (AVG) and the sample number
(N) is incremented. The current AVG and N are both
displayed on the bottom line of the LCD.
Although N can increment up to 250, only a maximum of
64 INDEX readings (N064) can be used to generate the
running AVG. If more than 64 readings are taken before
the short-term memory is cleared, the screen will display
AVG=- - -. However, deleting an INDEX reading from
short-term memory (thus causing a new AVG to be
calculated) does not free up memory space for storing an
additional reading. In other words, the average is not
calculated if the trigger has been pressed more than 64
times without clearing the average (see Keypad Operation,
p. 8).
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