THe BME280 and BME680 can only measure Pressure at the location of the Sensor. If you compare the sensor measurements you get with Pressure reported by the Weather Bureau, the values will not match, because the Weather Bureau provides only pressure readings for certain standard conditions, mainly at an Altitude of 0 Metres above mean Sea Level, 15 Degrees C. Barometric pressure decreases by about 12 hPA for every 100 metres above mean sea level, and this is often used to determine altitude eg. in Aircraft. It also varies with Temperature and Latitude to a small extent. The easiest way to get your altitude is to consult a topographic map. There are several tools available online, also some GPS systems can be coaxed to give you that information. Wikipedia will provide you access to mathematical formulae that allow you to calculate a calculated calibrated value for your reading based on a known altitude, as though you are located at Sea Level. Good luck with that.
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