EMIT, thank you for your interesting extensive answer.
If I understand it well, by using the LPC laptop, crews end up using CONF 3 when most of the time 2 or even 1, for a mere flex degree or even a single knot, would be as good if not better.
So I’m glad we’re still old fashion by using the paper performance charts where it is definitely easier to keep an overall view. And I can hardly see anyone entering a paper chart 100 tonnes off !?
Also, with a book, one guy extracts some figures, then closes the book. When ready the other guy proceeds with its own independent calculation, usually both results don’t even differ enough to worth mention.