The experience point scale (or XP scale) is a module setting that alters the experience point awards for killing creatures. This is set, using a slider in the Toolset, by the builder. This allows the awards to range from no experience to twenty times what is called for by D&D rules. (When a module is set to no experience, there is usually custom scripting in place to give out awards.)
The XP slider in the Toolset
The slider is found in the "Advanced" tab of a module's properties. The setting is expressed as tenths of what is called for by D&D rules. That is, a value of 5 means experience is half (5/10) D&D normal, while a value of 20 means experience is twice (20/10) normal. The slider ranges from 0 to 200, and defaults to 10 (or normal experience) for new modules. For comparison: the XP scale is 10 throughout the original campaign, 15 throughout the Shadows of Undrentide campaign, and 150 or 100 in the Hordes of the Underdark campaign (150 in chapter 1; 100 in the other chapters).