Here's the system we use in greater detail:
Assume that it takes N sessions to gain a level. And, for a given skill, a character can learn at most K ranks each level (e.g., if the cost is 2/7, then K=2, and if the cost is 3/3/3, then K=3).
At the end of each session, the character gains one "free" rank in every skill used that session. However, a character cannot have more than K "free" ranks beyond their current purchased ranks (learned ranks). Moreover, the character cannot have more than N "free" ranks in any skill.
When a character gains a level, we first eliminate any "free" ranks whose DP cost is greater than the base cost (normally the cost of the first rank). For example, if a character has two "free" ranks of Riding (cost 2/7), we eliminate the second "free" rank (i.e., the character is only expected to learn one rank of Riding). But, if a character has three "free" ranks of Fire Law (cost 3/3/3), we don't eliminate anything.
We then compute the DP cost of the "free" ranks. If the total cost is greater than the character's available DP, then additional "free" ranks must be eliminated until the cost of the "free" ranks equals the available DP. If the total cost is less than the character's available DP, then additional skill ranks can be purchased normally (or Stat Gains or Talents can be purchased).
In essence, when a character gains a level, the character must first spend DP to convert "free" ranks to learned ranks.
Exceptions:
- Body Development is used whenever a character takes damage, and Power Point Development is used whenever a character casts a spell. However, the base cost for these skills is 0 (i.e., you are never obligated to convert "free" Body Dev or PP Dev to learned ranks).
- Languages are only used when a Communications maneuver is required, and once a character has 10 ranks the base cost becomes 0.
- Maneuver in Armor is used whenever the character suffers a moving maneuver penalty for the armor; once a character has maxed out skill (for that AT), the base cost becomes 0.
Comments:
In our current game, the characters are gods. Each god level corresponds to five normal levels, and N is 5-7. Thus, if a skill is used in four sessions, the character can learn four ranks of the skill because the DP cost doesn't increase until the 6th rank is purchased. In effect, the characters are gaining one level almost every session. But, they're gods.