Units

[anastis]

Units are not appropriately displayed on the front end.

Furthermore, it would be nice to include the units inside the dropdown to ease the user. E.g. Standard (Kelvin)
In fact, most users want to pick a unit, not a unit system. That's what your labels say too. So just list the units, not the systems.

One more. Order them in order of expected preference/usefulness to most people. Kelvin should be last, unless your plugin's primary audience is scientists.