Keuffel & Esser Paragon Transit with Case K&E Transit

I know next to nothing about this piece. My husband explained to me how it is used. He has another one that he actually uses for his business. This one, however, I just may display depending upon the value and its history (if I learn about it.)
According to the ebay description, "it has high transmission coated optics and is in very good condition." Further, the ad goes on to state that the transit does come in its case. However, the instruction manual and the tripod are both absent. These numbers were offered for the transit: No. 740043/ Ser.# 515079.
I am interested in learning how old this piece is, along with a little lesson in its history, and finally its value. Any help would be greatly appreciated! Pictures of the piece can be found at the auction website.