Map: 144 fingerprints, 7 walks over 3 stretches, 2 outings.

Each outing held out in turn, and its scans located from the other outings:

                                by networks  and by signal  settling ties choosing the path
  scans held out                        144            144            144               144
  placed on the right stretch           136            137            136               136
  placed across a mark                    8              7              8                 8
  landed on the wrong stretch             0              0              0                 0
  not on the map                          0              0              0                 0
  mean error, of a stretch              17%            18%            17%               18%
  median error, of a stretch            16%            17%            16%               17%
  mean error in metres                 23 m           24 m           23 m              23 m
  median error in metres               22 m           22 m           22 m              22 m

  A scan that landed on the wrong stretch is not a small error, it is a different street,
  so it is counted apart rather than averaged into the distances. One placed across a mark
  is on the stretch next door, a few metres past the mark the two share, and its error is
  measured through that mark. Settling ties places each scan with the scans before it
  breaking a tie between two stretches. Choosing the path takes the likeliest path through
  them, which can overrule the scan itself.
