Plumb Bobs
The plumb bob is a tool to measure O verticality. Used in surveying and construction sites, a pendulum of an inverted cone with a weight of 0.2 to 1 kg is hung with a thread and gravity is used to determine the vertical. Usually a plumb bob is a pendulum. It comes in a variety of colors, shapes, and sizes, but is used with hanging threads and retainers called catches. Some of them are in sets. The catch not only winds up the thread, and has a mount for wooden parts, a magnet for iron parts, and various types such as a type that can be attached with a single action on concrete and aluminum frames, and a type that is not slippery even if you wear work gloves, etc. There is also a windproof plumb bob that has a plumb bob in a tube for measurements in windy places.