HELP!!!! Values?

Good day all! I have a line on a couple of interesting bits of WWI British militaria. One is an RFC (Royal Flying Corps) cockpit watch. This is not inset into the instrument panel, but a pocket watch style timepiece designed to be put into a special bracket or holder in the cockpit. The other is a officer's compass complete with the case and shoulder strap. I have no idea of fair market values for these things and whether an offer I make is insultingly low or so high I diddle myself. Any thoughts or input would be most welcome.