General Tools and Instruments DAF4000 - Manual (Page 13)

Comments:
7. If QNH figure is steady (is not flashing) this indicates the current relative pressure (QNH), credible because deduced from a
meteorologically slow variation.
8. The QNH sign flashes if this pressure has changed since the last cal bration.
9. If the QNH figure is flashing, it indicates the QNH pressure entered at the last calibration.
10. A rise in altitude or a meteorological variation when the recording is not active makes the QNH figure flash.
11. Cal bration of the QNH or of the altitude (known datum) makes it possible to re-adjust the Mini Airflow in relation to the measured ambient
pressure. This varies continually according to the altitude and the current meteorological conditions.
12. The only reference for the Mini Airflow is the air pressure which it is measuring, from which it deduces the altitude. Any variations in this
pressure makes the altitude change : 9 metres per hPa a low altitudes, 14 metres at 5,000 metres, and this is why it is necessary to
calibrate as often as possible to maintain a cred ble display (even airline pilots have this to comply with!).
9
T This is valid if the
M
Valid if the M
I
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9. Recording modes DAP4000
WHICH MEANS : The three recording modes operate in the same way and are connected. They display under
different forms one of the 48 pressure measurements stored each hour. By default : 24 h are displayed.
The record stores just the pressure on the sensor, the QNH or the altitude displayed is calculated, depending on the
current calibration.
Trend : This is the variation in pressure over the last 24 hours (or 48 hours, or 1 hour etc.). This is valid if the
Mini Airflow is in the same place (same altitude). A negative figure indicates a drop in pressure (arrival of a
depression), a positive figure, an increase (anticyclone). Pressure naturally varies during the day, and the
weather trend is more accurate at 24 hours or 48 hours (same time of the day).
QNH : This is the relative pressure at 24 hours ago (or 48 hours, etc.). Valid if the Mini Airflow is at the same place
and is recal brated.
Altitude : If you set off for a mountain walk or go paragliding, you can check the altitudes achieved hour by hour. The
altitude will be accurate if you force the QNH calibration of the Mini Airflow on the weather pressure that was
present when you recorded.
Display of a particular moment in the record :
Example: you want to know the trend, the QNH or the altitude 12 hours ago. Keep the button pressed down, then when 12 h
appears on the large digits, release it.