I clicked the X box next to each of the four mic cal files which closed them. I was just testing the various options. However, there is no way to make them visible again. You need to add something to fix this. Right-clicking on the Mic Cal Files label at the top of where the mic cal files are listed, and a popup that says, "Show Mic Cal Files" would do it. I am surprised that there is no way to bring them back and that no one has said it is a problem. I had to uninstall REW and reinstall it. That's not good.