A1: It is Nickel.
Q2: How to calculate the input resistance?
A2: ((1024+2*Serial_Port_Reading)*10000)/(512-Serial_Port_Reading), unit is ohm, Serial_Port_Reading is the value display on Serial Port(between 0~1023)
Q3. Where can I find technical support if I have some other issue.
A3: Please send an email to firstname.lastname@example.org.