Alternate UV

An UV set (map) is a definition on how a certain texture (skin) is applied to a 3D model. Some SCS vehicles have more than one UV set.

Usually; the first UV map is the regular one, where you can simply paint the whole vehicle model. The second (alternate) UV set usually is mirrored; i.e. you paint one half of the vehicle and your skin is automatically applied to the other half of the vehicle model.

This is not usually required for ETS2 models. However, some ATS vehicles may require this option to be ticked.

It is recommended to have this option off by default. If your skin doesn't look correct in game, then you should try ticking this option prior to exporting your mod.