The idea is for a very rapid indication of lift and sink without
the delay of some filtering systems (although it does filter).

https://www.indiegogo.com/projects/xc-tracer

XC Tracer is an advanced flight instrument for paragliders, using
data from an 9-DOF IMU, from a pressure sensor and from a GPS to compute the
real time climb rate and altitude, avoiding the undesired time lag that
conventional variometers have due to data filtering.

... of course the variometer indicates the climb / sink rate with beeping tones.
It is very easy to fly in thermals with XC Tracer, since what you feel and what
the variometer indicates do perfectly match.

As a paraglider pilot and designer since more than 25 years (right now working
for Gin Gliders) I was always stunned that the principle how a hang glider
variometer works has not changed since I learnt to fly paragliders. Variometers
measure the rate of change of altitude by detecting the change in air pressure
(static pressure) as altitude changes, and a filter “smoothes” the signal in
order produce a usable beeping tone that indicates the climb and sink rate. But
this filtering leads to an undesired time lag. While flying in thermals the
variometer may still indicate a good climb rate, but in fact this may no longer
be the case, it’s just because of the time lag that the variometer still beeps,
indicating a false climb rate. You can feel this when flying, there is sometimes
a discrepancy between what you feel and what the variometer indicates.

My idea was then to make just a variometer that also uses the vertical
acceleration in order to calculate and indicate the vertical climb rate in real
time, with no time lag.

An attitude and heading reference system AHRS consist of microelectromechanical
systems (MEMS) gyroscopes, accelerometers and magnetometers on all three axes.
Using all the information from these sensors it is possible to calculate the
orientation of the device in space, and therefore calculate the gravity
compensated vertical acceleration. A Kalman filter then estimates the altitude
and climb rate, using the vertical acceleration from the AHRS and the pressure
from the pressure sensor.

That worked very well, the variometer had no time lag, but then when talking
with friends they had the idea to integrate a GPS, then an SD card, then a BLE
module for that the flight information can be sent to a phone or a tablet.

This is how the idea of XC Tracer was born.

Thanks to Tom Payne.