I don't like things which use apparatuses because they introduce a dependency (and since this scheme is for use in extreme/unusual circumstances, it's especially likely that Harry would not have leisure time or access to his pouch) and they make part of the process observable, hence, easier to realize the existence of & reverse-engineer.
A fully mental PRNG is doable under all circumstances in under a second and is unobservable except via Legilimency (which if it isn't blocked, means one is screwed anyway since one can just be False-memory-charmed into remembering having done the verification*).
* Kripkenstein would approve!
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 116.
There is a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)