How Barometric Varios Work
A barometer is only capable of informing about pressure changes. Assuming a vertical translation (up/down) caused these, those pressure changes will be translated to altitudes. And the changes in altitude will be derived to calculate a climb rate. For a vario that is based solely on a barometer or a so called barometric only vario,
😯 changes in altitude / pressure need to happen before they can be detected 😯
Read that again please :-)! And these pressure changes only then can be translated into altitude changes or ultimately a climb rate which is what the pilot is really after. Having said this it should be clear that
⏳ a barometric vario needs time to actually integrate pressure readings ⌛
Time to get enough readings to reliably separate noise from signal. No matter what algorithm, whether it is a plain moving average, an exponentially weighted moving average or even some Kalman Filter, there is an inherent delay and a trade off between the accuracy and reliability of the climb rate and the integration time needed to calculate that climb rate. With that kind of setup a vario becomes solely dependent on the readings of one sensor.
Remember, a basic vario for paragliding uses the variation in pressure to calculate the difference in altitudes and from that difference the climb rate. However, that difference in altitudes will need to happen first which is why a barometric vario, one that is based on pressure alone, will be delayed, always! It can only indicate lifts or changes in altitude that already happened ¯\_(ツ)_/¯
That said, there are other sensors that can be used to calculate the change of the climb rate. And again it is about relative change rather than absolute values.
Acceleration - the INSTANT in the vario
To understand how an instant variometer works, imagine you just got into an elevator. (Thermals can actually be seen as our elevators to cloud base.) You pushed the very last button to get to the top (cloud base), closed your eyes and now you wait for the ride to begin. What will you be able to tell from your senses...?
Now, you naturally feel once the elevator starts accelerating. In this case you are experiencing a
🔝 Positive G-Force: your climb rate is expected to increase! 🆙
which results in a higher vertical speed. The start is actually like entering a thermal.
Of course, you also feel once the elevator starts braking or more technically, decelerates. In this case you are experiencing a
⬇️ Negative G-force your climb rate is expected to decrease! ⬇️
which results in lower vertical speeds and ultimately no speed.
So whenever you are accelerating (positive or negative) your climb rate will change. But what is more important, you are anticipating the change in climb rate before any barometric variometer could have made that calculation from altitudes and hence changes in pressure.
😃😃😃
⚡ Gravity changing is INSTANT ⚡
But what can you tell about the climb rate from the elevator going up at constant speed, once the acceleration (and deceleration phase to be correct) is finished. Can you tell how fast you are going up, your exact climb rate? No, you can’t! Without any visual clues it is impossible. Which is why we need the barometric climb rate calculated from changes in pressure due to changes in altitude. You cannot have an instant vario without using the pressure sensor of your smartphone.
🤐🤐🤐
⏳ change of altitudes is NOT INSTANT ⌛
Now, taking the instant part from gravity and fusing it with the not so instant part from pressure is the basic idea of an instant vario. Best of both worlds, plain simple.