I've been attempting to measure some stuff and trying to be careful about what I feed into my microcontrollers. I've had difficulty figuring out how to keep things within perfect limits, though.
For a project I'm working on currently, I drop down to nearly -1V for a short period of time (<1µS), but I might expect larger drops under some conditions.
This is the output of an op amp, so it's already buffered, and it does slightly better when I clamp it with a couple of zeners, but can still measure negative voltage where I don't want it.
(keep in mind, I'm a total noob, so many things I might be wrong about many things I'm saying)