anchor.diff:  "nhd_14705830","swimms","maxdepth",2.4384
   "nhd_14705838","swimms","maxdepth",1.524
   "nhd_14705866","swimms","maxdepth",3.9624
  -NA,"swimms","maxdepth",2.1336
  +"nhd_14705884","swimms","maxdepth",2.1336
   "nhd_14705902","swimms","maxdepth",2.4384
   "nhd_14705890","swimms","maxdepth",3.9624
  -"nhd_14707328","swimms","maxdepth",3.048
  +"nhd_14705890","swimms","maxdepth",3.048
   "nhd_13135515","swimms","maxdepth",3.9624
   "nhd_14707256","swimms","maxdepth",1.524
   "nhd_14707274","swimms","maxdepth",1.2192
   "nhd_14707274","swimms","maxdepth",2.1336
   "nhd_14707274","swimms","maxdepth",2.1336
  -"nhd_14705752","swimms","maxdepth",1.8288
  +"nhd_14705748","swimms","maxdepth",1.8288
   "nhd_14705758","swimms","maxdepth",1.524
   "nhd_14705778","swimms","maxdepth",1.8288
   "nhd_14707898","swimms","maxdepth",1.524
  
positive.code: "nhd_13118702","swimms","maxdepth",7.62
  "nhd_13118860","swimms","maxdepth",3.048
  "nhd_13118862","swimms","maxdepth",1.8288
  NA,"swimms","maxdepth",2.4384
  NA,"swimms","maxdepth",3.6576
  "nhd_13399151","swimms","maxdepth",10.668
  "nhd_13078255","swimms","maxdepth",10.668
  "nhd_2646624","swimms","maxdepth",NA
  NA,"swimms","maxdepth",1.524
  "nhd_14768092","swimms","maxdepth",5.7912
  "nhd_6842889","swimms","maxdepth",4.2672
  NA,"swimms","maxdepth",7.62
  "nhd_13346456","swimms","maxdepth",9.4488
  "nhd_6808274","swimms","maxdepth",4.572
  NA,"swimms","maxdepth",3.6576
  NA,"swimms","maxdepth",1.8288
  "nhd_13391775","swimms","maxdepth",1.524
  "nhd_120053690","swimms","maxdepth",12.192
  NA,"swimms","maxdepth",1.8288
  "nhd_6842851","swimms","maxdepth",3.3528
  "nhd_13393323","swimms","maxdepth",9.7536
  "nhd_14445892","swimms","maxdepth",2.1336
  "nhd_6816970","swimms","maxdepth",4.2672
  "nhd_13393393","swimms","maxdepth",4.572
  "nhd_13343132","swimms","maxdepth",NA
  "nhd_13394427","swimms","maxdepth",7.62
  "nhd_13391707","swimms","maxdepth",1.524
  NA,"swimms","maxdepth",4.2672
  NA,"swimms","maxdepth",16.1544
  "nhd_1813425","swimms","maxdepth",10.668
  "nhd_120053487","swimms","maxdepth",8.5344
  NA,"swimms","maxdepth",1.8288
  "nhd_6819676","swimms","maxdepth",2.4384
  NA,"swimms","maxdepth",2.8956
  "nhd_13395083","swimms","maxdepth",0.9144
  "nhd_2028595","swimms","maxdepth",NA
  "nhd_6792321","swimms","maxdepth",8.2296
  "nhd_1816133","swimms","maxdepth",13.716
  "nhd_13345756","swimms","maxdepth",18.5928
  NA,"swimms","maxdepth",3.048
  "nhd_13631715","swimms","maxdepth",NA
  "nhd_6792433","swimms","maxdepth",10.9728
  "nhd_1813737","swimms","maxdepth",2.4384
  "nhd_9029847","swimms","maxdepth",3.048
  NA,"swimms","maxdepth",7.62
  NA,"swimms","maxdepth",2.4384
  "nhd_13393591","swimms","maxdepth",4.8768
  "nhd_13393821","swimms","maxdepth",8.2296
  "nhd_1797539","swimms","maxdepth",3.3528
  NA,"swimms","maxdepth",3.6576
  "nhd_12173086","swimms","maxdepth",8.5344
  NA,"swimms","maxdepth",0.6096
  NA,"swimms","maxdepth",NA
  "nhd_9035963","swimms","maxdepth",2.7432
  NA,"swimms","maxdepth",1.524
  NA,"swimms","maxdepth",1.8288
  "nhd_1852669","swimms","maxdepth",8.2296
  "nhd_2647960","swimms","maxdepth",3.6576
  "nhd_9035869","swimms","maxdepth",12.192
  
negative.code: "nhd_13079171","swimms","maxdepth",2.7432
  "nhd_6808160","swimms","maxdepth",3.048
  "nhd_2267173","swimms","maxdepth",14.3256
  "nhd_1813543","swimms","maxdepth",5.1816
  "nhd_13291056","swimms","maxdepth",7.62
  "nhd_6808272","swimms","maxdepth",10.668
  