The hedonimeters on the right display mappiness users' happiness in real-time, compared against the all-time average.
Below, happiness levels are charted hour by hour over the past week.
As imagined in 1881 by the economist Edgeworth,
... let there be granted to the science of pleasure what is granted to the science of energy; to imagine an ideally perfect instrument, a psychophysical machine, continually registering the height of pleasure experienced by an individual, exactly according to the verdict of consciousness, or rather diverging therefrom according to a law of errors. From moment to moment the hedonimeter varies; the delicate index now flickering with the flutter of the passions, now steadied by intellectual activity, low sunk whole hours in the neighbourhood of zero, or momentarily springing up towards infinity. The continually indicated height is registered by photographic or other frictionless apparatus upon a uniformly moving vertical plane ...
(David Colander, 2007. Edgeworth's Hedonimeter and the Quest to Measure Utility. Journal of Economic Perspectives 21 p. 217. JSTOR)