An apparatus for determining a characteristic, such as body mass index number, for a person includes a housing having a panel with an edge portion, an intermediate portion, and a window formed in the intermediate portion. A member is movably secured to the housing and a peripheral portion of the member extends from the housing adjacent the panel edge portion. Indicia that indicates incremental units of a first characteristic is disposed on either the panel edge portion or the member peripheral portion. Indicia that indicates incremental units of a second characteristic is disposed on the other one of the panel edge portion or the member peripheral portion. Indicia that indicates incremental units of a third characteristic is disposed on the member and is viewable through the window. Movement of the member to align first indicia units with second indicia units causes display of third indicia units via the window.