What is the smallest unit of time an atmega328 can accurately measure?
Depends on the clock speed. In general, it is one timer tick of a /1 timer, which is the clock speed.
Note that this would be impossible to sustain - a lot more work is needed to setup another capture event.
No, I don’t need to sustain it nonstop. I just need it to be very precise when I’m using it as a wheel encoder. Check out my other posts in the project topics.