Electrodes and Calibration: Understanding References and Their Differences

Client:
Are your electrodes already calibrated?

Technical Advisor:
Hello,
No, it is not possible as calibration depends on your device. However, they are measured.

Client:
What is the difference between the 1681 and the...

Technical Advisor:
And the?

Client:
198

Technical Advisor:
None.

Client:
Why different references then?

Technical Advisor:
For internet referencing purposes.