You are bidding on a JASCO watch case battery test ammeter made in the late 1920s. The original nickel plating is nice all around.  It reads 0 to 30 amperes, per the scale.  It is designed for testing of 6 volt wet A batteries used with early battery sets from the 1920s. It measures 2 3/8 inches in diameter, and 3/4 inches thick.  It is a nice accessory item for your collection.  Shipping weight is 10 ounces.  Please see my other auctions for more interesting radio and audio items, and tubes.