The XP system is one of the last core things that need to be hammered out. Once that's done, the core of all three games will be pretty much done. So here are my thoughts. This is just me thinking aloud at this point and reverse engineering what we already have.
Now that careers/traditions have been standardized, we know that each grade adds 4 attribute points, 2 skill ranks, and one exploit. Assuming those three things are roughly equal, that means that we can easily assign a point value: 1 point per attribute point, 2 points per skill rank, and 4 points per exploit (12 total). That gives us the base value of a career grade and its elements.
A starting character typically has 5 career grades. That defines his maximum dice pool, too. So a starting character is Rank 5. (This also gives us space for weaker critters without having to delve into fractions).
Adding a career grade to a creature or a character just adds one rank. Simple.
The tricky bit is non-career derived abilities and the like. A dragon or an elephant have high attributes but no career grades (unless you choose to add career or tradition grades to them). So that's where we go back to our point value system to derive the value of the critter. Remember, 12 points is one rank.
So, we take...
Total attribute points + (total skill ranks x 2) + (exploits x 4)
...and we divide the total by 12.
For example, let's take our old friend, the Tyrannosaurus Rex.
64 attribute points [64], 1 skill rank [2], 1 exploit [4] = 70.
70/12 comes to 5.8. Let's say we round up, so that's 6.
Hmmm. Feels low compared to a starting character. The attributes derive most stats, but not SOAK, so maybe we need to accomodate that separately. I'm not sure how right now, though.
Let's try another. A hill giant.
78 attribute points [78], 2 skill ranks [4], 2 exploits [8] = 90
90/12 comes to 7.5. Round up to 8.
A puny little goblin.
23 attribute points [23], 4 skill ranks [8], 2 exploits [8] = 39
39/12 comes to 3.25. Round up to 4.
A swamp dragon.
140 atribute points [140], 6 skill ranks [12], 8 exploits [64] = 216
216/12 comes to 18.
So, stuff this doesn't accomodate: SOAK, and equipment.
Now that careers/traditions have been standardized, we know that each grade adds 4 attribute points, 2 skill ranks, and one exploit. Assuming those three things are roughly equal, that means that we can easily assign a point value: 1 point per attribute point, 2 points per skill rank, and 4 points per exploit (12 total). That gives us the base value of a career grade and its elements.
A starting character typically has 5 career grades. That defines his maximum dice pool, too. So a starting character is Rank 5. (This also gives us space for weaker critters without having to delve into fractions).
Adding a career grade to a creature or a character just adds one rank. Simple.
The tricky bit is non-career derived abilities and the like. A dragon or an elephant have high attributes but no career grades (unless you choose to add career or tradition grades to them). So that's where we go back to our point value system to derive the value of the critter. Remember, 12 points is one rank.
So, we take...
Total attribute points + (total skill ranks x 2) + (exploits x 4)
...and we divide the total by 12.
For example, let's take our old friend, the Tyrannosaurus Rex.
64 attribute points [64], 1 skill rank [2], 1 exploit [4] = 70.
70/12 comes to 5.8. Let's say we round up, so that's 6.
Hmmm. Feels low compared to a starting character. The attributes derive most stats, but not SOAK, so maybe we need to accomodate that separately. I'm not sure how right now, though.
Let's try another. A hill giant.
78 attribute points [78], 2 skill ranks [4], 2 exploits [8] = 90
90/12 comes to 7.5. Round up to 8.
A puny little goblin.
23 attribute points [23], 4 skill ranks [8], 2 exploits [8] = 39
39/12 comes to 3.25. Round up to 4.
A swamp dragon.
140 atribute points [140], 6 skill ranks [12], 8 exploits [64] = 216
216/12 comes to 18.
So, stuff this doesn't accomodate: SOAK, and equipment.