Vernier Sensor

[sojkic]

f is the value you compute. What you actually need are r, r1, r2, f1, f2. And yes, r is the value returned by readRawValue().

Where do I get the value of f1 and f2?

[skoehler]

I told you already. You apply a known force f1 and read the raw value r1.
You apply a known force f2 and read the raw value r2.

You chose what f1 and f2 are.

[sojkic]

I told you already. You apply a known force f1 and read the raw value r1.
You apply a known force f2 and read the raw value r2.

You chose what f1 and f2 are.

Please try again to explain what is f1 and f2? I want measure frictional force. My experiment will be look that I will drag subject on a different desktop. I don´t know force. I understand r is from method readRawValue() and r is measure current value. f1 is a force to be applied? If yes, so I don´t know. I'm sorry for me.

[skoehler]

You have to calibrate the sensor. I'm not even sure, whether linear interpolation is the right method.
In short, calibration is to figure out the raw values for several scenarios, in which the actual value that the sensor SHOULD return (whatever unit, whatever you are actually measuring) is known. Otherwise, how do we know what a raw value of 123 even means?

I mean, I can probably explain, which raw value corresponds to which voltage on the analogue input wire. However, would that help you in any way? I believe it doesn't. So conduct some experiments. Write doen the raw values returned by readRawValue() and write down the what the sensor SHOULD have returned during that experiments.