When I bought my Saw Stop I did not get an extra cartridge because I am pretty careful around the shop and I did not think I would ever need one.
This morning, in a hurry, I grabbed the miter fence and moved it to the left side of the blade. Yeah I know to slide the bar so it does not hit the blade but like I said, in a hurry.
This could have been a pretty bad accident but it was just noisy when the saw stop did what it should.
Look at what a small nick the saw put in the fence!