What does as a rule of thumb mean?

The meaning of the rule of thumb means to apply a procedure that is easily learned and can be use d at once. It is not accurate or exact when determining a value or figuring things out. The phrase is taken from carpenters who use their thumb rather than a ruler to measure things. Others say that it refers to planting using your thumb to plant seeds in the field. Either way it’s all about estimating something that is not that accurate.