Michael Storms, a psychologist at the University of Kansas, had been studying sexuality and erotic fantasies, and his research seemed to point to some of these conceptual problems with the Kinsey Scale. He found that bisexuals engaged in as much heterosexual fantasising as heterosexuals and as much homosexual fantasising as their lesbian and gay counterparts. He ascertained from this that bisexuality seemed to somehow incorporate total heterosexuality and total homosexuality in a way not indicated by the Kinsey Scale. Storms also wanted to distinguish between bisexuality and asexuality. In 1980, he proposed a new sexuality scale using an x-y axis.
This axis is not a perfect tool for representing sexuality, and has been criticised for implying that asexuality is a 'negative' option, and completely separate from other sexualities. As we learned from the Klein Sexual Orientation Grid, sexuality is not just about who people have sex with. It is perfectly possible to be asexual as well as identifying with any other sexual identity.