The FOV slider has a degrees symbol next to the value which would indicate it's measured in degrees, but the actual value it displays is a percentage.

The attachment FOV.png shows the internal FOV value compared to the value displayed in the game's options screen. Internally, the FOV is stored as degrees as a value between 30 and 110; in the options screen it's displayed as a percentage between 0 and 100, despite the degrees symbol next to the value.

Either the value displayed in the options screen should be in degrees, or the degrees symbol should be removed.