How to measure QNH in Hecto Pascal using BMP085 sensor?

Hi,
I am using the sample of Adafruit library but, it show the QFE pressure only and in Pa (Pascal). I would like to have the QNH pressure in hPa. Can you help me?
Thanks

You didn't notice that the library has a readSeaLevelPressure function?

QFE = baromic air pressure, corrected for the height with an airfield as reference.
QNH = baromic air pressure, corrected for the height with sea level as reference.

I think the Adafruit library uses just one offset.
You could copy the library files into your project and add a second offset.

jremington:
You didn't notice that the library has a readSeaLevelPressure function?

this is a part of the sample of Adafruit...

Serial.print("Pressure = ");
Serial.print(bmp.readPressure());
Serial.println(" Pa");

// Calculate altitude assuming 'standard' barometric
// pressure of 1013.25 millibar = 101325 Pascal
Serial.print("Altitude = ");
Serial.print(bmp.readAltitude());
Serial.println(" meters");

Serial.print("Pressure at sealevel (calculated) = ");
Serial.print(bmp.readSealevelPressure());
Serial.println(" Pa");

however, both values are very close!
I work in Airport here in Brasil and today morning I perceved that my pressure is QFE value.
QFE was 947,4 hPa while QHN was 1024 hPa !

You can't calculate the sea level pressure without providing the pressure and altitude at your current location. That function reads the pressure from the chip and takes an optional parameter, the elevation, to do the calculation. If no parameter is supplied it assumes zero; in other words, it assumes you're at sea level, so the current pressure = the sea level pressure.

Try it again, only enter your actual elevation:

const float myElevationInMeters = 500.0; // put your real elevation here, in meters
Serial.print(bmp.readSealevelPressure(myElevationInMeters));

And hPa is just Pa divided by 100.