1. A marker digitally encoding a numerical value, comprising: a perimeter having a predetermined shape; a center; a plurality of references, spaced apart around the perimeter to determine angular displacement about the center; at least one concentric data track disposed within the perimeter, the shape of the track being substantially similar to that of the perimeter; a digitally encoded bit pattern associated with the data track, the location of a particular bit within the pattern being determinable as a function of angular displacement and distance as measured radially inwardly from the closest point associated with the perimeter.