I have the following problem

My Physical System
I have a sensor which changes resistance on application of force.

Experiments performed

In order to characterize the output of the sensor, I have done some experiments. In the one of interest here, I applied different forces and took 4 readings at each force step. Total force steps are 5.

My final graph is force on X-axis and magnitude of resistance on Y-Axis.

I want to analyze sensitivity of the sensor.

What I have tried
I tried to caluclute the sensitivity of the sensor using the acquired data in GraphPad. But there seem to be some error. i want to calculate it using manual mathematics now.

Kindly guide me how to do it. An example will be great.

Thanks for your time