How to get from the wavefunction to weighted states?

[Jarrodmccarthy]

I Have a question about how we arrive at the probabilities for the wavefunction collapsing to some specific value for an observable.

As far as I'm aware, the wavefunction is a superposition of possible states depending on the observable we try to measure.
Lets say I want to measure observable A,

What is the procedure for getting from the wavefunction to a set of possible outcomes with coefficients that weight the possibilities?

Apologies if the question isn't well formulated.
thanks in advance.

 

[bhobba]

Good question, but I am not quite sure exactly what you mean.

It may be how a superposition becomes a mixed state:
http://philsci-archive.pitt.edu/5439/1/Decoherence_Essay_arXiv_version.pdf

Or the why of the Born Rule (see post 137)
https://www.physicsforums.com/threads/the-born-rule-in-many-worlds.763139/page-7

Or even what the Born Rule is:
https://en.wikipedia.org/wiki/Born_rule

Thanks
Bill