[scala] Confusion about Unit

I'm confused about Unit. It seems that any type conforms to it even though it's populated by a single value? ...

scala> var a : Int = 24
a: Int = 24

scala> var u : Unit = ()
u: Unit = ()

scala> a = u
<console>:6: error: type mismatch;
 found   : Unit
 required: Int
       a = u
           ^

scala> u = a
u: Unit = ()

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Alan