Restaurant personnel call system - uses sphere floating in liq. contained in half-transparent half-opaque cylindrical housing

摘要

The restaurant call uptem consists of a table mounted cylindrical housing (1). The top half (1a) is transparent and the bottom half (1b) is opaque. The interior of the housing is filled with a clear liquid (3) and contains an indicating element (2) in the form of a red ball. The specific gravity of the ball (2) is less than that of the liquid (3). Thus the ball (2) is always in the top half of the housing; that is either in the transparent half or opaque half dependent upon which way up the housing is placed. The ball in the top transparent half can be used to indicate to a waiter that service is required.