Cannot set value in digital display

Hi,
I’m trying to measure the water level of a tank and for that I have used s71500 plc (CPU 1511C-1 PN). I’m using two digital displays to set the value using potentiometer and measure the present water level. But somehow I got some flickering thing in the digital display whenever I’m trying to set the value.

I’m new to factory IO. Kindly help me to solve the issue.