why summing block in simulink is not giving zero when the inputs have zero difference between them?

i am using the simulink sum block to calculate the difference between two inputs. but the block output is always non-zero even when the inputs are equal. although the output is very small, but this difference is further multiplied by a gain, which is ultimately resulting in a significant error. how to solve this? this problem is due to very precise calculation of difference between the two inputs. i am attaching two run time images of my model and a scope which is showing the actual difference between the measured inputs