Gary - The Datum 9520 series are Time Code Displays (discontinued). They have been appearing via government and military surplus via obsolescence sales. In addition to the 6-digit time display of the 9520 series, this specific model (-1000) includes the 3-digit Day of Year (DoY). I believe that all of the 9520 series support the Amplitude modulated carrier (IRIG B) timecode. Datum 9520-240 manual http://www.arsitec.com.br/arquivos/produtos/9520-240-manualF.pdf Datum 9520-647 manual ftp://50-199-14-216-static.hfc.comcastbusiness.net/electronics/testgear/time-freq/symmetricom/9520/9520-647-manual.pdf Since this Datum 9520 is discontinued, ITS (California) provides modern replacements, especially for F-16 fighter aircraft (9520-647 version). http://www.itsamerica.com/Files/tcdisp.htm greg Sent from iPad Air