Emotions can be distinguished on three dimensions: pleasant versus unpleasant, activated versus quiescent, and feeling dominant versus feeling vulnerable.
In the plane formed by pleasantness and activation, emotions lie approximately on a circle. Unpleasant emotions are further distinguishable in terms of domination versus vulnerability. Interestingly, no pleasant emotion with a name is associated with a sense of vulnerability.
The orderliness of emotions on the three dimensions inspired the idea of using an emotion-spiral to measure emotions. Studies by Heise and Calhan (1995) and by Heise and Weir (1999) used such an instrument for data collection.
The following shows an emotion-spiral measuring instrument for use on the World Wide Web. This example doesn't actually collect data; the Done button has no effect.