This chart shows the changing weight of one hive. For the first 10 days of May, the weight of the hive barely nudged up. But then, on the 10th of May, the hive started to pack on over 5 lbs per day. So what changed? Well, 10 May is the first day I saw blooms on the black locust trees in my area. These thorny trees are loaded with thousands of white flowers and are a powerful nectar source. They line many of the highways in Missouri, and a good locust bloom often makes a good year for beekeepers.
The point of showing this chart is that weight is the best way to track honey flows and dearths. When the weight goes up quickly, you've got yourself a flow. When the weight levels off and starts to fall, you're in a dearth and you should consider feeding. By using a scale, you don't have to inspect surrounding fields and forests for flowers, and there's no need to analyze whether your bees look "full" when they're flying back into the hive (I doubt this is effective). Plus you only need one in each bee yard, because if there's a flow on for one hive, there's a flow on for all of them.