RFC 387 Experience Implementing Net Graphics Protocol August 1972 System A System B (Absolute Coordinates) (Relative Coordinates) -1 -2 -3 -16 0 -1 -2 -15 -2 2 2 ... ...2 -2 2 2 ... 2 +--+--+--+--+---------+--+--+ +--+--+--+--+---------+--+--+ | | | | | | | | | | | | | | | | +--+--+--+--+---------+--+--+ +--+--+--+--+---------+--+--+ ^ ^ .0111 ...............11 = +1/2-e 0.11 ..............11 = 1-e .00 .................01 = +e 0.100 .............00 = 1/2 .00 .................0 = 0 0.00...............01 = e .111 ................11 = -e 0.00 ..............00 = 0 .100 ................ = 1/2 1.11 ..............11 = -e 1.10 ..............00 = -1/2 1.00 ..............01 = -1+e = -(1-e) 1.00 ..............00 = -1 -16 -15 Where: e = 2 Where: e = 2 -16 -15 Range: -1/2 to +1/2 - 2 Range: -1 to +1 - 2 I submit that one could interpret the requirement for absolute coordinate data to be in the range -1/2 to +1/2 - e as requiring that two different number systems should be used. Thinking along those lines, System A has the advantage that you never get handed a number out of range, which saves some checking worries. It also has one whole bit more of precision. I further submit that having two systems to contend with merely clouds the issue and requires extra coding. It makes more sense just to stick with System B above. Among the advantages in its use are: 1. The single system can handle both absolute and relative coordinates. Kelley & Meir