We often conflate states of being with emotion. Happiness, I would argue, is an emotion, whereas contentment is a state of being. I feel happy if I get some unexpected good news, but I am content if my affairs are in order, and I have a good network of people who care about me, etc. One can be happy at a particular moment, but generally depressed. Or a contented person can feel sadness, such as when a relative or friend dies. Trying to measure one's "happiness" is conceptually incorrect, in my opinion. What we should measure is the contentment one feels with one's life. "Money can't buy happiness" is axiomatic to most people, but I disagree; money has bought me happiness many times, as in I enjoy my house, car, TV etc. But, money can't buy contentment; that can only come from a sense of inner peace.