Calibration

Get some standard reference solution for you local hydroponics grow store.  Also fill a spray bottle with distilled water for cleaning the reference solution off of the glass probe tip.   Do not touch the glass probes with your fingers, as it leaves oil residue that will influence your reading.

Two calibration points will be fine, pH 4 and pH 7.  Get some glass wear from the kitchen and add some reference solution.  Put the pH or ORP probe in the solution and wait for the value to adjust, it usually takes one or two minutes.  You can use the serial monitor on the Nanode ( un-comment out the #debug  serial.print function) to read the output of your pH and ORP probe.   After one point calibration, spray or rinse the glass junction with distilled water for a couple minutes before putting it in the other standard solution.

The ORP reading for the standard reference solution is as follows:

pH Value	mV Value	pH Value	mV Value	pH Value	mV Value	pH Value	mV Value	pH Value	mV Value
0	990	3	800	6	640	9	460	12	280
1	920	4	740	7	580	10	400	13	220
2	860	5	680	8	520	11	340	14	160

The ORP probe in the pH 4 reference solutions should read around 740 mV and the pH 7 reference solution should read around 580 mV.