http://www.lce.org/equipment/phmeter/phmeter.html (http://www.lce.org/equipment/phmeter/phmeter.html)
http://www.lce.org/equipment/phmeter/electrodes.html (http://www.lce.org/equipment/phmeter/electrodes.html)
http://www.lce.org/equipment/phmeter/phuse/phread.html (http://www.lce.org/equipment/phmeter/phuse/phread.html)