When using DSI pressure transmitters, it is necessary to use an Ambient Pressure Reference.  DSI’s ambient pressure monitors report the absolute observed pressure measured in the room where it is placed.  

Some barometers are calibrated to report barometric pressure adjusted to a sea level reading (known as relative ambient pressure).  Weather stations and some barometers reports the pressure as relative ambient pressure OR sea-level corrected barometer reading.  DSI’s ambient pressure monitors report the absolute pressure measured in the lab. 

For labs above sea-level, the absolute pressure (APR equipment) of the lab is lower than a relative pressure reading (barometer or local weather station).  

In the event you need to convert the relative pressure reading from a barometer or weather station to an absolute reading to enter into the Ponemah's barometric pressure value, you will need to subtract the values shown in the table below from the relative pressure.  Alternatively, you can use the attached Excel Workbook to determine the value to enter into Ponemah.  

For comparison to relative pressure reading (weather service and/or sea level adjusted barometers), the differences are summarized in the following table: