What is the traditional unit of sake volume called 'Issho'?

The traditional unit of sake volume known as 'Issho' is indeed equivalent to 1.8 liters. This measurement is significant in Japanese culture, particularly in the context of sake consumption and packaging. The literary and cultural references to 'Issho' often appear in ceremonial contexts, serving as a standard measure for sake bottles commonly found in the market, such as the 1800 ml bottle.

The other choices represent various volumes that do not align with the traditional sake unit. For instance, 10 liters, 5 liters, and 3 liters are not historically recognized units for sake and are generally not used in sake production or traditional serving practices. Therefore, understanding that 'Issho' specifically refers to 1.8 liters is crucial when discussing sake measurements and their relevance in both commercial and cultural maritime contexts.