Now, Eisen had a mana crystal that in itself was capable of producing flames in the way described by the magic circle that the old man placed into it. And the thing about it was that any single part of it could to an extent. The whole piece was needed to produce the full power that the magic circle would have been capable of displaying. But if Eisen split the crystal up into two equal parts, each of them would be able to push out flames at half the full power.
Seeing that this actually worked like he 'remembered', although he didn't actually vividly remember any instances of ever doing this but just rather the raw information about it, Eisen merged the two halves back together and got started on working on more magic inscriptions.
