Need help in creating device for calibration of flex sensor

Hi, I’m a beginner in using the Arduino IDE software and still learning about the Arduino and its related components. I have a project which i need to calibrate the flex sensor according to the angle of the sensor. I have succeeded in getting the result which when we flex the sensor, we will get the value of ADC which i then convert to voltage.

However, problem arise due to the calibration as the device i made to check the angle of the flex sensor in order to get the ADC value is very improper and poor in design. Hence, the reason i came here is to ask all the kind people here how do i calibrate the flex sensor properly so that the result that i get is more legitimate.

Here i attached the pictures of the device i made. I do agree with what my teacher said that the design is very poor and improper.

Thank you