This P28 Aurora is Strathearn's Large size of this Aurora series. Sizes range from over 2.7" to over 3.0". There are twelve divisions or ribs and each has seven bubbles with the top ring of bubbles forming a cap at the top of the weight. Colors made in are Grey, Red, Green, Blue and Black and I've found no other colors yet. Circa 1965 to 1979. Quanities produced each year are unknown at this time.