Set this to your local forecast pressure at sea level. This will offer you slightly improved accuracty for your flight, although it's not 100% essential every little helps!

Xcweather.co.uk is a decent place to grab pressures from for your location and time.

This is the altitude above the launch pad altitude where the altimeter will trigger itself into recording / flight mode.

The altimeter keeps a constant average of the pressure while waiting for launch, it uses a simple algorithm and the pre-flight buffers to do this. The most recent 120 samples (~4 seconds) are ignored so your pre-trigger altitude won't effect the ground baseline.

For almost all uses we suggest keeping this on the 25 Meter (~82 feet) default settings. If you want to test your altimeter by throwing it in the air, or are planning a very low flight you may want to lower the setting.

The altimeter runs at 50Hz however you can record every sample or every X samples in order to extend the log time. For example if you set the ratio to 1 it will save 1:1 samples, or if you set it to 3 it will save 1 in 3 samples.

This is the maximum samples the altimeter will log per flight. When it reaches this amount it will stop and save the recording.

This setting is how the altimeter decides to stop recording. You can choose either 450 (~9s) or 900 (~18s) samples stable or it will record until the max samples limit unless you press the BUTTON in Manual stop mode.

The samples stable method waits for the devices altitude not to change for the set number of samples. This is defined by not changing by more than +/- 1.0 meters for 98% of the samples, it's a reliable method to stop the recording after landing within 8-10 seconds (300 sample) or 16-20 seconds (600 sample).

Oversampling is a internal setting of the BMP 390 pressure sensor. It is how many samples are taken for each reading. By taking multiple samples for each pressure reading the altimeter reduces noise and increases the resolution of the output.

The sensor can run at 50 samples per second in 4X mode, so we suggest leaving it in this mode as it will offer the highest accuracy.

The IIR filter is another internal sensor for the BMP390 pressure sensor. It is a Infinite impulse response filter used to enhance pressure measurement accuracy by reducing noise. It's primarily for smoothing out rapid pressure changes.

We suggest not setting this too high as it will cause delay to changes in altitude if set very high.

This filter is a software Kalman filter that runs on the altimeters processor.

The Kalman filter uses a prediction step based on a system model and then a correction step using new measurements to refine its estimate, it creates accurate most certain results from data with noise in it.

The filters on the pressure sensor can cause it to lag very slightly behind the Accelerometer and Gyroscope data. The Sync sensors option detects how far out of sync these sensors are. It then corrects the Acceleration and Gyroscope readings to match the pressure sensor.

This is the orientation you intend to install the Altimeter in your rocket. It's needed to ensure completly accurate angles and orientation charts and reports. Check out the Manual for more information on this.

The IMU filter, or fusion filter takes the data from each axis of the Gyroscope and Accelerometer to calculate the Pitch, Roll, Yaw and tilt angle from vertical. These filters can build up some discrepency over time so it's important to calibrate your sensors to minimise this.

This is prevention against accidental launch detection.

With this disabled the launch is based only on pressure and something that creates a low pressure can trigger the flight by accident. For example pulling your nose cone off can even trigger it.

With this enabled the rocket also needs to have seen 8 samples (0.25 seconds) of acceleration above this setting in the last 3 seconds as well as the pressure drop to trigger. There is a backup trigger of 1.05 seconds of altitude being above the launch detect setting too.

There are very few situations where this option would cause issues, so we suggest leaving it on.

When enabled, the altimeter locks out recording for a set period after power on to prevent false triggering during setup.

A fixed temperature value used for altitude calculation when the external temperature sensor is disabled or not connected.

If an external MT1 temperature sensor is connected, this controls whether it is used for logging only or also for altitude calculations.

A custom name or tag assigned to this device for easy identification.

The language setting configured on the device.

Controls what happens after recording. Standard shuts down normally, Delayed keeps WiFi on for 30 seconds after landing, Stay on keeps the device powered on.

The brightness level of the LED indicators on the Mercury. Lower values save battery.

WiFi transmit power level. Higher gives better range but uses more battery.

Controls whether the device enters low-power sleep when idle.

Monitors battery voltage during the flight.

The cloud group / category this flight is assigned to.

Enable or disable the external I2C PCA9685 servo expansion board.

The oscillator frequency of the PCA9685 chip. Default is 25000000 (25 MHz). Adjust only if your board has a different crystal.

The minimum pulse width in microseconds for the servo range. Standard servos typically use 500-600 µs as minimum.

The maximum pulse width in microseconds for the servo range. Standard servos typically use 2400-2500 µs as maximum.

The PWM frequency for all servos on the board. Standard servos use 50 Hz.

The total mass of the rocket after motor burnout (dry mass). This is used for the ballistic prediction of apogee altitude. Enter the mass without the motor propellant, or the mass at burnout.

The aerodynamic drag coefficient (Cd) of the rocket. This is used with the rocket area to calculate aerodynamic drag during coast. A typical model rocket has a Cd of 0.4 to 0.8. You can find this value from OpenRocket or RockSim simulations.

The cross-sectional reference area of the rocket in square meters. This is typically the area of a circle with the body tube diameter. For example a 38mm tube has an area of approximately 0.00113 m².

The specific gas constant for dry air, used in the atmospheric model for altitude and density calculations. The standard value is 287.05 J/(kg·K). You shouldn't need to change this unless you know what you're doing.

Enables or disables the active air braking system. When enabled, the Mercury will deploy air brakes via the configured servo channel to try and reach the target altitude. Firmware 2.1+ required.

Which servo output channel the air brake mechanism is connected to. GP6 and GP7 are the two onboard servo headers, I2C channels are for an external servo expander board.

The speed at which the air brakes deploy. The Mercury gradually increases the servo angle until the predicted apogee matches the target rather than going full on/off. This setting controls how quickly it ramps up to full braking.

The target apogee altitude in meters. The air brake system will try to slow the rocket so it reaches this altitude.

The percentage over the target altitude to aim for until within 15% of the target. This helps prevent undershooting if the prediction is slightly off early in the coast. For example, with a 1000m target and 5% early adjustment, the Mercury will aim for 1050m until it passes 850m.

The air brake system activates after burnout, but won't engage until the rocket has reached this percentage of the target altitude. This prevents the brakes from deploying too early when predictions may be less accurate.