A friend gave me an Efratom M-100 Rubidium standard to check out and calibrate. I found a couple manuals to download, and they appear to be pretty complete. Even have schematics!! The unit belonging to my friend is p/n 70502-7. The manuals appear to be for p/n 70502-1. Close to the front of the manual is a statement: "A model M-100 with a part number other than 70502-1 is a modified unit". My question is thus: Is there a document anywhere that has a comprehensive list of modifications for the M-100? Or, at least a description of the modification on the -7 unit? It may well be just mechanical or cosmetic in nature, and have no bearing on the operation (I haven't fired it up yet). It appears to be physically identical to the illustrations of the 70502-1 in the manual. Any help or comments are welcome. Dave M