I need to find out how much this pocket watch is worth?

All I know is it's my late grandpa's old pocket watch. I found it in an old box in his attic. I cannot open the backside, but I can open the front. It's a Waltham make, and there is a set of numbers on the inside cover. I have no clue how to tell when it was made. It is solid gold, and it has some engravings on the front of what looks like three arch ways, with two flowers above them. On the front there is a marking that almost looks like a crest, but more fancy around the edges. Any help on figuring out the year and price ranges on these would be great! Thank you!