Fix typo
diff --git a/Doc/lib/libdecimal.tex b/Doc/lib/libdecimal.tex
index c4095c9..c0a2cc7 100644
--- a/Doc/lib/libdecimal.tex
+++ b/Doc/lib/libdecimal.tex
@@ -938,7 +938,7 @@
         d, da = d+da, da+32
         t = (t * n) / d
         c += t
-    getcontext().prec -= 10
+    getcontext().prec -= 9
     return c
 
 def exp(x):