An optional compression algorithm used in some Group III facsimile machines, MR scans and compresses the first line using Modified Huffman (MH) compression. Subsequent lines are scanned and compared to the first line, and only the differences (deltas) are encoded and transmitted.This process continues for some predetermined number of lines in a group, at which point the process is reset and the first line in another group is encoded using MH, and so on. MR is particularly effective if there are few differences between lines in a document. See also compression, facsimile, Group III, and MH.