I am considering the absolute digital pressure gauge type LEO1 with a 4 bar absolute range. If the resolution is 1mbar as stated on the data sheet and I am reading a -1 bar pressure, would the pressure gauge read 13mbar absolute?
If the atmospheric pressure happened to be 1013 mbar absolute then yes the LEO1 would read 13 mbar absolute in theory, however there is the uncertainty / accuracy of the LEO1 to consider in addition to the resolution which is +/-0.2% FS. So for this range it might be out by +/-8 mbar although the repeatability should be much better than this. Also since the atmospheric pressure is constantly changing, a negative 1 bar g reading will constantly change after being converted to an absolute reading.