Happiness is a subjective concept and, therefore, hard to quantify. But a variety of researchers have sought to do so.
They vary in their views of what happiness consists of, though they generally agree that it is more than mere pleasure. One hedonic view sees it as the aggregation of multiple positive emotions.
How do I know my tank is full?
Owning a tank brings the added bonus of a slice of nature to your home or office. It also provides the owner with a chance to watch their fish thrive and flourish in a natural habitat. There are many things that contribute to a happy fish; including plenty of room to swim, a good diet and water conditions, a clean tank, a completed nitrogen cycle, peaceful tank mates, appropriate plants, gentle owners and a tank size that fits the species of fish.
Oftentimes the tank will be full when the gauge points to the F mark or when the nozzle is turned off. However, as pointed out in another answer tank geometry can make the point at which a tank is full slow down or even stay at the top for a little while after the pump stops.
What is the difference between a full tank and an empty tank?
Many schools of philosophy are skeptical of the importance of happiness. Some of these doubts center on relatively weak conceptions of happiness, such as a belief that it refers only to pleasant experience or a mental state that philosophers generally call “emotional well-being” (or simply “emotional health”).
Other worries focus on the idea that valuing happiness is self-defeating, in that people may value things that are not conducive to happiness. This concern, often referred to as the hedonistic paradox, also appears in arguments against the classical Utilitarian emphasis on the pursuit of happiness as the primary or sole good for human beings.
A final worry focuses on attempts by states to promote happiness directly through social policy. Some people fear that such efforts are paternalistic in the sense of taking away citizens’ autonomy. Others are concerned that such initiatives fail to consider important factors in achieving well-being, like access to food and shelter. Nevertheless, these concerns do not appear to have been seriously tested in empirical research.