Altitude Changes even when not moved.

Hi:
I’m running the BME680 experiment and I’m using the local sea_level_pressure to try to get altitude.  My readings are not stable.  I’ve got the experiment running in my house and my house is about 12 feet above sea level locally.  Is there any reason that the altitude would change?  Could it be the the atm pressure is changing?  Appreciate any help.  Love working with the BME680.  It is a really neat chip.

Just my thoughts. I do not claim to be very knowledgable in this field.
 
The atmospheric pressure is not fixed. You get hi and low front that is the engine of weather changes.
I read pressure any where from 1010 to 1018, I compare it to the official sites, it usualy compares very well. I have the bme680
When a cell of air get loaded with moisture it falls down and leak to neighboring cells on the surface of earth. in such case the cell went from high to low pressure.
The change in pressure can get significant but there should be a carpet value for sea level and that what is used in the example

Omar, thanks for this answer.  I’m more concerned about altitude however.  The response from the ESP 32 changes even though the position of the ESP 32 never changes.  It appears to change with the pressure in the room.  I would hope that it would always give me the 12 feet above sea level because that is where it is.  Any thoughts?

it does change but within the datasheet
my house on the coast as well

Hi.
Thank you all for your valuable inputs.

The altitude is calculated taking into account the current pressure and sea level pressure at the moment.
There are always fluctuations on the pressure measured from the sensor, hence you’ll have altitude fluctuations.
Additionally, the sea level pressure can also vary. If you use the same sea level pressure reference all the time, you may also have changes in altitude calculations. The reference sea level pressure is hardcoded on the sketch, so it is always the same.
I’m not an expert in these weather topics, but I think this explains the fluctuations.

Regards,
Sara

Thanks Sara and Omar.  I think to make this work accurately that the sea level pressure would have to be continually input from an external source.  The BME680 appears to be accurate when I compare with what I get from local weather sources with pressure data available.

Yes. I think that would be the solution.
Getting the updated sea level pressure from an external source.
Regards,
Sara

In aviation, when you are leaving an airport you set the altitude of the airport on the altimeter. When you climb higher than 18,000 feet you set the altimeter to 29.92 inches of mercury so that all aircraft are using the same setting. When you are descending through 18,000 feet approaching a new airport you then set the altimeter to the value given to you by the air traffic controller there which should show you the airfield height above sea level when you land. You might be able to get the local barometer setting from a nearby radio or TV station but you would have to update it regularly, or just buy a barometer. Good luck. Doug.

Thanks for sharing that, Doug.
Regards,
Sara

Tech Note 142 – Calibrate a BME280/680 Pressure Sensor or Barometer is a “YouTube” video by G6EJD – David.
Good information to pass along; covers subject very well.  
Could indoor air flow from a heating “duct/register” be causing a change in Barometric Pressure; in turn affecting the altitude reading?  I woulder if altitude changes would occur in a stationary location outdoors. 
 
William
 
 

Will check it out.  Thanks.