I don't understand this rule : what the difference between success and magical success? If the die indicates the rune, it's always a success no ?
A magical success is a better class of success. p21 of the core rulebook offers some helpful guidance.
Some commentary below from Jacob Rodgers, who was the one of the Lead Writers on the Rivendell supplement. I follow his guidance of treating a Magical Successes as an extra 6 at a minimum.
viewtopic.php?p=64216&hilit=magical#p64140
"Yeah, it is very important that the narrative impact be appreciated and rewarding. This isn't just the Elf rolls Awareness and the LM answers 'the distant folk are Riders of Rohan' but that the 'the distant folk are Riders of Rohan, 105 in total, with three horses that are riderless, being guided by others. Their spears are very bright but their shields are battered, as if they have recently been in battle. Their leader is very tall. Almost all of them are blond-haired and, though it's hard to tell from here, grim-faced.' That gives a lot more detail, and, more importantly, provides some excellent hints about how a Council might proceed and what questions to ask.
If you have to put a numerical value to it, consider it worth at least one more Tengwar." - Jacob Rodgers"
viewtopic.php?p=64216&hilit=magical#p64216
"Well, to be fair to you, it was an accurate statement. I did add a little bit to the example, but I like drawing examples from the books (even if they will be applied slightly differently) just because folks can hook into it, and say 'ah, yes'. The important part is that the Magical Success should deliver something clearly more than a regular Gandalf success. Gandalf is "you did as good as anyone else could do in such circumstances". A Magical Success (especially via Skill of the Eldar) is "you did unbelievingly better than anyone else could do in such circumstances"."