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 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).