The "zero" pressure may need to be taken at regular intervals, if you are not doing that now, not just on start up as has been discussed in previous posts. Or if an ambient BMP280 sensors has not been included. However, it was stated in a post that the ventilator is a timed cycle design and the pressure sensor is not used in the actual control of the ventilator. In that case the absolute accuracy of the pressures may not be as much as an issue.?
Looking at January 2020 data at San Francisco airport, in one day the atmospheric pressure changed 0.2 inHg, or 10.4 cmH2o. over the whole month the atmospheric pressure varied by 0.87 inHg, or 30 cmH20.
Tom, wb6b
