This article is an examination of the evolution of a skill formula.
GDW's house system, as used in Dark Conspiracy (modified by the players' screen), has a simple formula to determine a character's competence with a skill: the level of the skill (1-10), plus the level of the governing stat (also 1-10). However, if a PC attempts to raise the skill higher than the stat, the cost of doing so (in experience points) is doubled.
This worked, but from my point of view had some problems. First, I didn't like the cost-doubling; when generating a character, it's easy to forget which stat governs which skill. My solution to this was to declare that skill levels above the governing stat were half as effective - thus with a stat of 6, a skill level of 8 would be evaluated as if it were level 7.
The second problem was that I tend to regard skills as being more important than raw stats. To this end, I halved the stat value before adding. The skill formula at this point was:
Stat/2 + Skill, unless Skill>Stat, in which case Stat/2+(Skill-Stat)/2+Stat.
This was duly implemented in the character spreadsheets, and the system lumbered along for a while. However, when I came to restart the game recently, I noticed that the high-skill formula was equivalent to Skill/2+Stat. Since I was also doubling the range, this came out neatly to Skill+Stat*2 for high skill, and Stat+Skill*2 for low skill; which in turn was simplified to:
Moral: algebra is good. Simplify. And don't try to design formulae in spreadsheets; the if() and lookup() functions are too tempting.
Roger Burton West