The phrase "tested formula" means that a method or process has been tried and proven to be effective. It refers to an approach that has been experimented with and shown to work successfully. Full definition
Finally, by sticking to the tried and tested formula of save points, which are relatively few and far between, you are always on edge. (16bitdad.com)
Remove the bottle and, once again, shake it before testing the formula on your wrist. (howtoadult.com)
We also use a combination of market - leading analytical, ecommerce, marketing and trading expertise to deliver a tried and tested formula for highly successful car parking businesses. (magairports.com)