At work we have these magnetic blocks which have arms attached to them for dial indicators. They are use to hold the dial indicators like an extra pair of hands. They work great. My question is how do they work!? The magnetic block has a switch on it. This switch will turn the magnet on or off. When it is on, it is quite strong. When off, you wouldn't really know there was a magnet there at all. There is no power applied to it, so this is completely a mechanically switching of its internal components. I am amazed at how strong the magnet is, and that it can be turned off. How does this work? Is is simply an application of a shield inside the housing? Specifically, the ones we use are made by Mitutoyo. I do not have a model number. They are referred to by the manufacturer as magnetic blocks. I am very curious about their operation. Does anyone have insight? Thanks.