I have this Gruen watch, an NDK crystal, marked as NDK61. As I understand it, that means it was manufactured in Jan 76. Works fine, shows wear, and is a massive watch, it weighs the same as my Pulsar Big Time. I would be willing to sell it, but I have no idea what might be a reasonable price. Although there may have been many made, it appears to be rare these days since I can't anything close to it in any forum, gallery, or book. How does a person establish a resonable price totally in the dark about value? Obviously, condition plays a part in value and like my Pulsar, it shows its age. Going for a best price on ebay doesn't tell me anything concerning it's value. I need some assistance where I can start to look for a value. Hopefully, it will have more value than the $4.50 I invested in batteries.