 How to plum the depth in one minute? If you want to know how to tell the depth of a pond, you will need a plummet. What is a plummet? A plummet is a weight on a hook, used to show the true depth of water when float fishing. Knowing the depth prevents the angler from accidentally putting the float too far away from the hook, or so close to the bait is suspended mid-water unintentionally. Plumbing or plummeting depth can also show how to tell if your bait is in weed, silt or clear ground. See the link. If you like catch and release fishing, don't go fishing without one of these. Fishing at the right depth helps to catch fish in the lips and reduce deep hooked fish by instantly letting you know when a fish picks up a bait. Heavy plummets are best for beginners, as they are easier to feel when they hit the bottom. Used properly, a plummet will show the angle of the varied depths, contours and habitat of an otherwise invisible lake or riverbed. And for a float fisherman, the plummet is the most important item of tackle in their box.