John; Try the tool Peter found. I thought the GPS-12 lacked a serial port and the GPS-12XL had both a serial port and external antenna port. Both good to have for a differential station. "Message: 9 Date: Mon, 8 Apr 2019 01:52:20 +0000 From: John Reid<reid.john@hotmail.com> To:"time-nuts@lists.febo.com" <time-nuts@lists.febo.com> Subject: Re: [time-nuts] Garmin GPS12XL V3.51 Message-ID: <CY4PR13MB1208ADEA24712E636EDBE1B9F82C0@CY4PR13MB1208.namprd13.prod.outlook.com> Content-Type: text/plain; charset="utf-8" I checked today the GPS12XL I have, and that came up with a date in August 99, before dying a few minutes later. Firmware 4.57. The only thought I had was that the GPS 12 (still working, still showing "19" as the year) was bought new around 2002 with a differential receiver. Perhaps there was something different for that? John" -- Joe Leikhim Leikhim and Associates Communications Consultants Oviedo, Florida JLeikhim@Leikhim.com 407-982-0446 WWW.LEIKHIM.COM