Since I am on the "digest plan" I am a little slow to respond. As a user of sources in the early 50's, I can say that mc stood for millicuries ( if in caps, for Magacuries ) the "u" was used for micro. -- Roy C. Craft CHP 1707 Pecan St. Bay City, TX 77414 rcraft@tgn.net (409)245 9991