Vaisala HM40 - Manual (Page 32)

31
Avoid Condensation and Rain
If the humidity sensor element becomes wet, the meter
cannot measure until the sensor is dry again. Avoid rain
and conditions where condensation can form on the
sensor.
Do not replace the transport protection cap if the probe
or the cap is wet, since it will prevent the probe from
drying.
Do not touch the sensor or blow on it to dry it out.
Calibrate the Meter Regularly
It is recommended that you calibrate the HMP113 probe of
the HM40 meter once a year, or if you have any reason to
believe it is no longer within its accuracy specification.
See section Calibration on page 35.