Read this and answer the question. If the question is unanswerable, say "unanswerable".

One of the earliest sexual orientation classification schemes was proposed in the 1860s by Karl Heinrich Ulrichs in a series of pamphlets he published privately. The classification scheme, which was meant only to describe males, separated them into three basic categories: dionings, urnings and uranodionings. An urning can be further categorized by degree of effeminacy. These categories directly correspond with the categories of sexual orientation used today: heterosexual, homosexual, and bisexual. In the series of pamphlets, Ulrichs outlined a set of questions to determine if a man was an urning. The definitions of each category of Ulrichs' classification scheme are as follows:

When did Karl Heinrich Ulrichs develop this classification scheme?
in the 1860s