Since I have a Tracor 527E I am not going to bid on the following link. I have bought two items with very good results and have nothing to do with the seller. I suspect based on his location that this is NASA material. The unit has a FRK Rb in it. Bert Kehren _http://www.ebay.com/itm/Argosystems-AS210-RM-Rubidium-Time-Frequency-Calibr ation-System/332265338742?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m14 38.l2649_ (http://www.ebay.com/itm/Argosystems-AS210-RM-Rubidium-Time-Frequency-Calibration-System/332265338742?ssPageName=STRK:MEBIDX:IT&_trksid=p20603 53.m1438.l2649)