Today in 1967, US Patent 3311267 A was issued, an invention of James E. Houston, Ryals E. Lee,and George M. Norman, for their “Measuring Attachment for Beer Keg or the Like.” There’s no Abstract, but the description states that the “invention relates to the dispensing of liquids including beer from closed opaque kegs or containers subjected to pressure to discharge the contents and with regard to which it is desirable to be able to determine the amount of liquid contained at any particular time between the initial dispensing and exhausting of the contents of such keg or container.” There’s not much more, but they explain its object:

It is an object of the invention to provide a simple, practical, readily usable, measuring attachment for a beer keg or the like, which can be quickly applied and removed, and by means of which an immediate reading of the contents can be made at any time.