Why is scope output choppy?

Hi all.

I am downloading my simulink program to an Arduino Mega 2560.

I notice that the scope response in my simulink model is very choppy, and I've noticed that this choppiness shows up when the program is running off of the arduino as well. Why is this? I need precise control for my physical system.

If I have the exact same model but run it without attempting to download to the simulink model, the scope results are perfectly smooth.

Any help would be greatly appreciated!

Thanks,