Stretches walked more than once, and how far apart the passes put the networks:

  "Rivera y Brito del Pino" to "Rivera y Avenida Doctor Francisco Soca", 142 m
    17:03:05 to 17:04:40, walked there
    17:04:45 to 17:06:20, walked back
    11 networks heard on more than one pass
    the passes disagree by 9% of the stretch (13 m) on average
    shift in the direction of travel: 5% (6 m), which is what a scan's lag looks like

  Mean disagreement over 1 stretch: 9% of a stretch.
  That is the error bar on placing an access point along a route, measured against nothing but the walk itself.
