Distance Unit Use this option to specify the unit to use for computing distance between markers. Units are described in the table below: Unit Specify this unit to: Markers Define LD blocks in terms of the number of markers separating the pair, not the physical distance between markers. Location Variable Unit Define LD blocks by the physical distance between markers in terms of the variable specified in the Annotation Location Variable field. To Specify the Distance Unit: Select the desired unit by clicking within the appropriate radio button.