This Application Note on the NE555 & NE556 Timers from
Signetics Corporation is one of the most Useful Resources
I've been able to find thus far. Unfortunately it is
"OUT of PRINT," that is to say, I have been unable to find it in
~.pdf file format (or any other); only in an old Signetics
Data Book, hence the poor quality of this rendition.
This is not the conplete note; more pages will follow; as well as
a smaller & cleaner version.