I've used this tool you mention, yet no one was able to tell me the name of it.
A small brass device that flips open and has a little nail on the tip.
I was told in grading that it measures the 'slope' of the grain, and will not detect spiral checking...
I have to remember to take more pics, for today I had the perfect example of a straight grained larch timber with said spiral checking, which I come across sometimes.
Too bad I have a 3 day weekend and I'm not going to be at work tomorrow..sitting on the beach instead ....
