Contributions are welcome

I won't say no to any physical, chemical or mathematical constant as long as

1. It's not there already. Please check out terms for those already in the core, like e.

2. You can find a reference for it, preferably Wikipedia, but anything else is OK. That means: if you are Bob and want to add Bob's constant, it's probably not a good idea. Please add the reference as a comment behind.

3. You write a test for it too.

4. If possible, add an example where it could be used.

5. If it's got some one-letter equivalent, please alias it to that letter too. For instance, plancks-reduced-h is aliased to ℏ.

If your constant is used, like c, as a measure, you can also add a postfix function so that it can also be used that way.