What do I have here?

I don't believe it's radium, however the watch itself spikes and continues to climb if left alone. I've tried measuring the case by itself, the case closed with the watch inside, and watch separately and it is indeed the watch that's giving it off. I'm also aware that the GMC-300S reads lower compared to the 600 series. For CPM, the watch almost reached 65CPM.

I understand that Phinney-Walker produced watches with radium paint on the hands, but I also understand that over time the radium burns out and no longer glows and the color is no longer green. Could it be tritium instead?

I can't find the watch anywhere online except for one ebay listing with very little information about it, and no information of the year produced. Any help would be appreciated! Please let me know if this isn't the place to list it :)!