Abstract: Apparatus for simultaneously indicating the bio-rhythm curves which illustrate the emotional, mental, and physical cycles of a person comprising three slide elements, two of which are overlayed on the third and are transparent to simultaneously display all three curves in relationship to each other. The slides are mounted on a board having a transparent window with reference marks formed across in relation to a calendar scale indicating the days of the month and year. A reference scale is positioned near the start of the year for indicating the set point of the sliding scales and starting indicators are provided for calculating the starting day of each person's cycle in reference to his birthdate. A preferred embodiment has two scales such that the bio-rhythmic cycles of two persons may be compared to determine when they are compatible and incompatible.