Psychiatrist Fritz Klein was a respected researcher, author of "The Bisexual Option" and editor of the Journal of Bisexuality. He invented the Klein Sexual Orientation Grid (KSOG) in 1980.
Klein's Sexual Orientation Grid was developed "in an attempt to better ... understand the complexities of human sexual attitudes, emotions and behaviours". Klein thought that Kinsey's original scale was useful to a degree, but he was concerned that there is far more to sexual identity than just who one has sex with. He also added the dimension of time to acknowledge that one's sexual identity can change.
Klein's representation still has its flaws: it doesn't recognise a bisexual identity or a bisexual community, assuming that bisexuals have a mixed gay/straight identity and associate with gay and straight people equally. It relies on the gender binary of male and female, which can cause confusion for anyone who has recently transitioned to the opposite sex (or doesn't self-identify with either sex).
What the Klein Sexual Orientation Grid does well is to open our minds to abandon easy definitions of our sexual identity and, instead, to think of our sexual identity as being multi-faceted. It can be thought of as a starter to greater awareness of sexuality. Many people have suggested additional dimensions to the Grid.
You can explore your sexual identity with the Klein Sexual Orientation Grid online quiz!