Use a +1 to -2 scale for Exp apt instead of 100 to 160.

It is now consistent with the skill apts. Races with a -1 apt require 18% more
experience to reach a given XL than races with a +0 apt do.

The old apts were converted to the new scale as follows:

100         -> +1
110,120     ->  0
130,140,150 -> -1
160         -> -2

1 files changed, 5 insertions, 3 deletions

diff --git a/crawl-ref/source/skills.cc b/crawl-ref/source/skills.cc
index 5267c31ada..f73bd76c8a 100644
--- a/crawl-ref/source/skills.cc
+++ b/crawl-ref/source/skills.cc
@@ -49,12 +49,14 @@ static void _train_skills(int exp, const int cost, const bool simu);
 
 // The progress of skill_cost_level depends only on total experience points,
 // it's independent of species. We try to keep close to the old system
-// and use an experience aptitude of 13 as a reference (Tengu).
-// This means that for a species with 13 exp apt, skill_cost_level should be
+// and use an experience aptitude of 130 as a reference (Tengu).
+// This means that for a species with 130 exp apt, skill_cost_level should be
 // the same as XL (unless the player has been drained).
+
+// 130 exp apt is midway between +0 and -1 now. -- elliptic
 unsigned int skill_cost_needed(int level)
 {
-    return exp_needed(level, 13);
+    return (exp_needed(level, 1) * 13) / 10;
 }
 
 // skill_cost_level makes skills more expensive for more experienced characters