Scca

I'm quite sure this is the case, the camera just moves but the FOV is the same.

You are probably right, the Iron Sight currently in the calculator for Vanguard is for AR.

This is not related to the discrepancy shown by the calculator. This discrepancy shows you what the sensitivity/360 distance is with the calculated sensitivity is compared to the target sensitivity/360 distance, and is caused by the lack of decimal support by the game.
The inaccurate slider note means that when you set the slider to say 3.3 it might in reality be anything from for example 3.21 to 3.39. This is the case for a lot of games unfortunately, and if there's no config file option there's not much you can do about it.
This will make the actual sensitivity differ from the calculation, but usually not by a significant amount. Although this will vary depending on your sensitivity. If your target sensitivity is for instance 0.2, and the actual sensitivity is 0.29 due to the slider being inaccurate, you will get a significant difference since it's 1.45 times higher.
 

Yes, just a plain text file with the correct name. You can just copy any of the other config files and rename it and change the content if you are unsure

Trigonometry
https://www.wolframalpha.com/input?i=tan((PI*74)%2F360)*cot((PI*66.6)%2F360)

No, it says to set it under the advanced video settings, i.e. in-game
That would be fov_desired 90, which is the default value.

Correct, this is updated now

What you said is correct, and it has to be this way to make any sense. If the scopes were matched to the hipfire of the output game you would not get any consistency unless you also match the hipfire FOV between the games.
Consider this example converting from Overwatch with FOV 103 to Overwatch with FOV 80: https://www.mouse-sensitivity.com/?share=43c8dace9347072001b6b2962b254eaf
The FOV change only affects hipfire, the zoom FOV stays the same. So the sensitivity (360 distance) for the zoom should also stay the same to keep it consistent. If they were matched based on FOV 80 instead, you would get a completely different sensitivity for identical zoom levels.
Click the reverse calculation button between the input and output game

Quake maybe ?

there's trepang2 for single player and f.e.a.r. combat (community run) for multiplayer if you like that style of game, and cube 2: sauerbraten and Urban Terror are also pretty popular open source (aka freeware) titles

Nice, updated it now.

I forgot to update the minimum value, fixed now!

Sorry, I missed this post. I've updated the sensitivity and added adjustable FOV now

Updated!

There's no universal way of doing this, how scopes scale varies across the board, and there no way of knowing how a specific game scales the scopes without analyzing every one of them, unless the game actually provides accurate info regarding this.
Scopes can scale these ways, amongst many others:
By dividing the horizontal FOV, so a 2X for a hipfire FOV of 90 is 45. Same as above, but for the vertical FOV instead. Actual optical magnification. As the three above, but not affected by changing the hipfire FOV. As the three top ones, but the base is not the hipfire FOV. A random FOV for each scope with no relation to the stated power or hipfire. A random scaling to hipfire. +many more The actual stated power of the scopes (2x, 3x etc) in the games are completely arbitrary when you compare different games. Sometimes even within the same game they do not make any sense compared to each other.
The only way is by manually analyzing everything, as I do when the scopes are added to the calculator.

Personally I think Battlefield 1/Battlefield V zoom system is the best and wish it did become the standard.
Your zoom level also ends up being a direct multiplier of your cm/360 (if using 0%). 1x = Hipfire, 2 x = cm/360 x 2.

As soon as I have access to the game. Unless there's any major changes it shouldn't take more than 0,5-1 hour.

Thanks for the report, I've rolled back a few changes to work on a fix, so it should work again now.

You can do like this: https://www.mouse-sensitivity.com/?share=511a55e13315803937c4b13988a5414d
This will keep the aim you convert from the same, and the hipfire and everything else will be adjusted to the conversion you select.

It's not in use.
No, you have to set each scope individually.

The game is showing you the 4:3 FOV, and not your actual FOV based on your resolution.

Correct.
It means that you need to pay attention to the special options and make sure you set them on/off in the calculator according to what you have in the game.

Vehicle sensitivity is just the transport vehicles, while the tank driver sensitivity is based on both this sensitivity and its own tank sensitivity. 
Due to how the plane sensitivity works it can't be added.

That was just an example entered by me.

For that you have to select the scope you want to see the 360 distance for and enter the settings for it, like in this example.
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