Relative barometric pressure does not match official source.
Your relative pressure likely does not match the official source because you have not calibrated it properly. You will need to reference your User Manual for correcting relative pressure.
To compare pressure conditions from one location to another, meteorologists correct pressure to sea-level conditions. Because the air pressure decreases as you rise in altitude, the sea-level corrected pressure (the pressure your location would be at if located at sea-level) is generally higher than your measured pressure.
Thus, your pressure may read 28.62 inHg (969 mb) at an altitude of 1000 feet (305 m), but the corrected pressure is 30.00 inHg (1016 mb).
The standard sea-level pressure is 29.92 in Hg (1013 mb). Pressure conditions greater than 29.92 inHg (1013 mb) are considered high pressure and less than are considered low pressure.
Most weather stations instruct you to find a reporting station near your location to identify the corrected pressure.