diff --git a/src/SparkFunBME280.cpp b/src/SparkFunBME280.cpp
index 31d5377..235e259 100644
--- a/src/SparkFunBME280.cpp
+++ b/src/SparkFunBME280.cpp
@@ -390,7 +390,13 @@ float BME280::readFloatPressure( void )
}
-//Sets the internal variable _referencePressure so the
+// Sets the internal variable _referencePressure so the altitude is calculated properly.
+// This is also known as "sea level pressure" and is in Pascals. The value is probably
+// within 10% of 101325. This varies based on the weather:
+// https://en.wikipedia.org/wiki/Atmospheric_pressure#Mean_sea-level_pressure
+//
+// if you are concerned about accuracy or precision, make sure to pull the
+// "sea level pressure"value from a trusted source like NOAA.
void BME280::setReferencePressure(float refPressure)
{
_referencePressure = refPressure;
@@ -406,7 +412,13 @@ float BME280::readFloatAltitudeMeters( void )
{
float heightOutput = 0;
- //heightOutput = ((float)-45846.2)*(pow(((float)readFloatPressure()/(float)_referencePressure), 0.190263) - (float)1);
+ // Getting height from a pressure reading is called the "international barometric height formula".
+ // The magic value of 44330.77 was adjusted in issue #30.
+ // There's also some discussion of it here: https://www.sparkfun.com/tutorials/253
+ // This calculation is NOT designed to work on non-Earthlike planets such as Mars or Venus;
+ // see NRLMSISE-00. That's why it is the "international" formula, not "interplanetary".
+ // Sparkfun is not liable for incorrect altitude calculations from this
+ // code on those planets. Interplanetary selfies are welcome, however.
heightOutput = ((float)-44330.77)*(pow(((float)readFloatPressure()/(float)_referencePressure), 0.190263) - (float)1); //Corrected, see issue 30
return heightOutput;
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