[Question] Type annotations in associated constants

I have an associated constant defined in my impl block:

impl Foo {
  const THRESHOLD: f32 = 0.8;
...
}

But when I try to use the constant in a method, like so:

(self.r as f32 / self.n as f32) > LinHash::THRESHOLD

I get this error:

error[E0283]: type annotations required: cannot resolve `_: std::cmp::Eq`
  --> src/lib.rs:55:22
   |
55 |         let t: f32 = LinHash::THRESHOLD;
   |                      ^^^^^^^^^^^^^^^^^^
   |
   = note: required by `<LinHash<K, V>>::THRESHOLD`

Can someone help me understand this error? Why doesn't Rust detect that the constant is an f32? And where does it expect me to add an annotation?