do relative calibration of baros with 1s delay

src/modules/sensors/vehicle_air_data/VehicleAirData.cpp

@@ -254,6 +254,10 @@ void VehicleAirData::Run()
 		}
 	}
 
+	if (!_relative_calibration_done) {
+		UpdateRelativeCalibrations(time_now_us);
+	}
+
 	// Publish
 	if (_param_sens_baro_rate.get() > 0) {
 		int interval_us = 1e6f / _param_sens_baro_rate.get();
@@ -325,6 +329,31 @@ void VehicleAirData::Run()
 	perf_end(_cycle_perf);
 }
 
+void VehicleAirData::UpdateRelativeCalibrations(const hrt_abstime time_now_us)
+{
+	// delay calibration to allow all drivers to start up
+	_calibration_t_first = _calibration_t_first == 0 ? time_now_us : _calibration_t_first;
+
+	if (time_now_us - _calibration_t_first > 1_s) {
+		_relative_calibration_done = true;
+		const float pressure_primary = _data_sum[_selected_sensor_sub_index] / _data_sum_count[_selected_sensor_sub_index];
+
+		for (int instance = 0; instance < MAX_SENSOR_COUNT; ++instance) {
+
+			if (instance != _selected_sensor_sub_index
+			    && _calibration[instance].device_id() != 0
+			    && _data_sum_count[instance] > 0) {
+				const float pressure_secondary = _data_sum[instance] / _data_sum_count[instance];
+				const float new_offset = pressure_secondary - pressure_primary + _calibration[instance].offset();
+				_calibration[instance].set_offset(new_offset);
+				_calibration[instance].ParametersSave(instance);
+				param_notify_changes();
+				ParametersUpdate(true);
+			}
+		}
+	}
+}
+
 void VehicleAirData::CheckFailover(const hrt_abstime &time_now_us)
 {
 	// check failover and report (save failover report for a cycle where parameters didn't update)

src/modules/sensors/vehicle_air_data/VehicleAirData.hpp

@@ -85,6 +85,7 @@ private:
 	void CheckFailover(const hrt_abstime &time_now_us);
 	bool ParametersUpdate(bool force = false);
 	void UpdateStatus();
+	void UpdateRelativeCalibrations(hrt_abstime time_now_us);
 
 	static constexpr int MAX_SENSOR_COUNT = 4;
 
@@ -132,6 +133,9 @@ private:
 
 	bool _last_status_baro_fault{false};
 
+	bool _relative_calibration_done{false};
+	uint64_t _calibration_t_first{0};
+
 	DEFINE_PARAMETERS(
 		(ParamFloat<px4::params::SENS_BARO_QNH>) _param_sens_baro_qnh,
 		(ParamFloat<px4::params::SENS_BARO_RATE>) _param_sens_baro_rate