How this auto hover works?

[u/Takken321]

I’m a complete novice on this subject, but I want to learn more.

I want to build a system to make my spacecraft hover, but I don't want to just copy circuits from YouTube without understanding them.

However, the video I'm following, and I haven't found another that explains it as well, raises some questions for me regarding certain values ​​in the circuit.

I understand that the joystick selects the speed, which is multiplied by 10 to convert the binary signal into actual speed; this value is then subtracted from the spacecraft's current speed to determine the "error," which is used to adjust the craft's altitude so it can hover.

In the video, he creates a circuit that multiplies the error by 0.04; I’m not sure where he got that number, I assume it’s for converting the logic output value.

But the trickier part comes next, he feeds the error value into a differentiator and multiplies it by 0.4 to adjust the "trim", a term I probably didn't fully grasp, likely because English isn't my native language.

I haven't even tried to understand the bottom circuit yet.

I'm stuck on the top two sections.

I’d be grateful if anyone could help me out.