Macrodata Refinement is the section of Lumon Industries where Mark, Irving, Dylan and Helly work. It is referred to by the abbreviation MDR. The sole task of a Macrodata Refiner is to identify groups of numbers on his or her computer terminal screen, fence those numbers off, and place the number groups in one of five 'buckets' on their screens, until all such number groups in a given file are identified.

It is not known what the files are for, what the numbers mean or what the goal of refinement is. The refiners only know that the work of Macrodata Refinement is mysterious and important.

Each refiner works on one file at a time. Files have non-descriptive names. Once loaded on the computer terminal, a file reveals an array of numbers on the screen, zero through nine, that extend in all directions. The job of the Refiner is to search the screen for groups of numbers that elicit emotions corresponding to Kier's four humors: Woe, Frolic, Dread and Malice, a skill that takes concentration and practice to master. Sometimes a number might jiggle a little, offering a clue to the Refiner.

Given the time and effort it takes a Refiner to complete a single file, there could be hundreds to thousands of such number groups in every file.

As the Refiner identifies each number group, he or she uses the trackball attached to the terminal to select all the numbers in a group which fences them off, and then drops that group of numbers into an area of the screen called Buckets. There are five Buckets on each screen labeled 01 to 05. Some quantity of each of the humors, labeled WO, FR, DR and MA, are represented in all five buckets. Refiners are given small perks when certain milestones are reached on a given file. At 25% complete, Refiners are given a blue finger trap; at 50% complete, an eraser with the Lumon logo, despite the absence of pencils in the office; at 75% the whole team is given a Melon Party, and at 100% the Refiner is given a caricature sketch.