High Magery and Enchanting

[Black Rose]

If it were me - and I can't imagine a situation were I'd let Accuracy +10 in a game I ran - I'd do this. Note that my approach focuses more on amount of FP in the enchantment more than some specific multiplier:

Accuracy/Puissance:
Bonus..Kromm's..Mine
+1....250......250
+2.....1K.......1K (+750)
+3.....5K.......5K (+4K)
+4....20K......10K (+5K)
+5...100K......20K (+10K)
+6...400K......40K (+20K)
+7.....2M......80K (+40K)
+8.....8M.....160K (+80K)
+9....40M.....320K (+160K)
+10..160M.....640K (+320K)

Fortify:
Bonus..Kromm's..Mine
+1......50......50
+2.....200.....200 (+150)
+3.....800.....800 (+600)
+4......3K......2K (+1,200)
+5......8K......4K (+2K)
+6.....32K......8K (+4K)
+7....128K.....16K (+8K)
+8....480K.....32K (+16K)
+9...1.28M.....64K (+32K)
+10..5.12M....128K (+64K)

Deflect:
Bonus..Kromm's..Mine
+1.....100.....100
+2.....500.....500 (+400)
+3......2K......2K (+1,500)
+4......8K......4K (+2K)
+5.....20K......8K (+4K)
+6....100K.....16K (+8K)
+7....400K.....32K (+16K)
+8....1.6M.....64K (+32K)
+9......4M....128K (+64K)
+10....20M....256K (+128K)

[Fred Brackin]

Originally Posted by kirbwarrior

Why is the cost of those spells multiply instead of adding? And by such a large amount? It seems to me that +1 is kinda cheap and +3 pretty expensive.

Because "normal" For Gurps when those costs were first worked out was a ST 13 guy with a broadsword.

Gurps was a lot less flexible in those days. It was pretty serious about limiting characters to 100pts at start, ST costs started going up at 14. Cost was doubled for increase after chargen and there was no Weapon Master or Power Blow or Imbuements to boost damage.

+3 was fine for Excalibur in those days.

[Pomphis]

And even in AD&D not all artifacts were +5. It was a time before Hackmaster+12 swords.

[Kromm]

Note that I just worked from the data GURPS Magic offers . . . I'm not saying that millions of energy points necessarily make sense (but skip to the end for examples where it might). You could decide that every level past the max just adds another increment of the max, so that the cost goes up linearly with level. That would be fine, too:

Accuracy/Puissance

+1 . . . 250
+2 . . . 1,000
+3 . . . 5,000
+4 . . . 10,000
+5 . . . 15,000
+6 . . . 20,000
+7 . . . 25,000
+8 . . . 30,000
+9 . . . 35,000
+10 . . 40,000

Fortify

+1 . . . 50
+2 . . . 200
+3 . . . 800
+4 . . . 3,000
+5 . . . 8,000
+6 . . . 16,000
+7 . . . 24,000
+8 . . . 32,000
+9 . . . 40,000
+10 . . 48,000

Deflect

+1 . . . 100
+2 . . . 500
+3 . . . 2,000
+4 . . . 8,000
+5 . . . 20,000
+6 . . . 40,000
+7 . . . 60,000
+8 . . . 80,000
+9 . . . 100,000
+10 . . 120,000

Remember that none of this is "official" or "canonical." Without a book that gets a playtest, these and other estimates might be broken, silly, or just the wrong way of thinking about the problem.

On the other hand, also remember that energy costs for enchantments are not comparable to those for non-enchantment spells. Enchantment energy can be invested incrementally, and come from quite a few slow, sure sources. If all mithronium gets 1 energy point/millennium toward items made from it, and global deposits of mithronium date back 4.5 billion years (about the age of the Earth), then a mithronium sword might get a free 4,500,000 energy if an enchanter takes the time to cast even the lowest level of the Puissance spell. And if an item is the epic blade of the defender of the realm, given to him by an emperor who knows secrets of mass magic that give him 1 energy point from each of the realm's citizens, it could have tens of millions of energy points in it.

The assumption "all magic items are made by enchanters using the standard rules, with no cheats or workarounds" is dodgy. Even in settings where this is mostly true, the assumption that archmages will be bound by the same rules is at best boring and at worst broken.