cost index
At my last airline cost indices were published seasonally and varied from destination to destination, but never more than a few units (ie between 18 and 30).
At present airline we use one standard cost index of 28. We tried 20 at one stage but all got fed up with the descent speed of 266kts, so have reverted to 28 which gices a rather handy descent speed of 280kts.
Amazingly unscientific considering the price of fuel!