Just to add to the math a little, suppose you did an 8*8 embark, which is pretty big, in a region totally made of stone (so every tile in engravable).
48*48 tiles in a region tile * 8*8 embark = 147,456 tiles per z-level
Now let's say you have one of those giant freakish elevation changes that gives you a site with 100 z-levels, and you actually have it on only one tile in the corner of the map, so every z-level is full of walls. You are going to have to dig a stairwell to each of the bottom 15 levels to get to any of the walls there, so in combination with the insane elevation change, each level has 147,455 walls, so the whole map has 14,745,500 walls, plus 147,455 floors at the top level.
Let's say you engrave each tile twice, once as a wall before mining it out and reengraving it as a floor, cheating to avoid engraver tantrums due to art defacement. We'll neglect the horrible amount of time taken for the player to do the designations for that kind of insanity and say they have a script doing it automatically. That means the walls count as 29,491,000 engravable tiles altogether.
That gives a grand total of 29,491,000 + 147,455 = 29,638,455 engravable tiles on this site, or 296,384,550 possible experience points gained from engraving the whole map.
Since the total experience required to reach level
x is 50
x(
x + 9), 296,384,550 experience points would put a dwarf all the way up to... something like level 2430.
So, would a level 2430 engraver have a 99.99% rate of masterpieces? Keep in mind that would be engraving 10000 tiles and getting 9999 masterpieces.
The formula for item quality based on level is... oh, damn! Look at that, 0x517A5D disassembled the game and figured out the exact formula, up to date as of 40d9, and put it up at
http://www.dwarffortresswiki.net/index.php/Quality. He actually put the relevant part of code up, annotated, hidden in a comment.
I guess Kael was just making shit up. "Lost the save" indeed.