Precision means that all of the unique parts must fit and work together in order for an organism to function. Only a very specific collection of parts tailor-made to work together will exhibit functionality.
When there are a lot of particular requirements (such as shape or chemical characteristics) necessary for a system to work, it is obvious that chance processes cannot fashion all of these parts and have them work together. These choices only come from a conscious intelligent being who understands what needs to be done and knows how to do it. Think of all the engineers who study created things in the natural world to solve their engineering problems.
So many aspects about living creatures involve precision. Molecular machines and embryonic development of body plans all display precision as do the metabolic reactions.