HP49-50G: gallonUK conversion into l

[Martin Hepperle]

Wikipedia says:
Imperial gallon as re-determined in 1895 and defined in 1963
4.546091879

More specifically:
In 1963, this definition was refined as the space occupied by 10 pounds of distilled water of density 0.998859 g/mL weighed in air of density 0.001217 g/mL against weights of density 8.136 g/mL (the original "brass" was refined as the densities of brass alloys vary depending on metallurgical composition), which was calculated as 4.546091879 L to ten significant figures.[5]

The precise definition of exactly 4.54609 cubic decimetres (also 4.54609 L, ≈ 277.419433 in3) came after the litre was redefined in 1964. This was adopted shortly afterwards in Canada, and adopted in 1976 in the United Kingdom.[5]