Abstract: An elongated hollow body of transparent material is provided and defines a closed cavity therein including a first elongated portion extending transversely of one end of the body, a second elongated portion disposed adjacent and at a 45.degree. angle relative to the other end of the body and a third elongated portion extending along the body and communicating corresponding ends of the first and second cavity portions. A quantity of liquid and a gas bubble fill the cavity and the cavity walls include first, second and third partial cylindrical wall portions spaced closely inwardly of first and second end surfaces and a longitudinal side surface of the body. The first and second end surfaces are disposed at 90.degree. and 45.degree. relative to the longitudinal side surface of the body and each of the surfaces includes indicia thereon defining the central area of the corresponding cavity wall portion in which the bubble may be seated.