Check out the Topcon Museum. It is helpful in determining the vintage of older instruments.

GTS-250W Precise, Durable. The GTS-250 series imparts the familiar quality of Topcon total stations for surveyors and construction professionals.

The 310 Series is listed as having been introduced in '1997'. Also, the GTS-310 series instruction manual is available, although at quick look, it appears to be un-dated. One of my elementary school teachers insisted that I always put my name and date on any paper I submit. It was only later that I learned to add a north arrow. download Taarup 307 Parts Repair Manual Saudi Aramco Bop Manual download free. here. Finally, there was a feature called Google timeline which would sort results based upon when they were created. Although the internet may have been in its infancy when the 310 series came out, I'd say you might figure something out using that tool.