A divergence appears at one point in ASTM C 94 Standard Specifications for Ready Mixed Concrete which allows a choice in the manner in which concrete will be specified. The specifier may: (1) provide a "recipe" giving the exact quantities to be used in batching the materials for concrete; or (2) state the required performance qualities needed in both the plastic and hardened concrete leaving the means by which these qualities are achieved to the ready mixed supplier. The first approach is commonly referred to as a "bag specification" and the latter is referred to as a "strength specification." The two methods are similar in that both stipulate slump, air content and maximum size of aggregate. They diverge, however, in the method of controlling the quality of the paste. The first- the "bag specification"- uses a cement factor; the second- the "strength spec"- uses strength. One disadvantage of the bag specification as it is used today is that it discourages the conscientious ready mix producer from striving for a low coefficient of variation. In the early days of concrete construction, concrete batching techniques and testing procedures were not sufficiently developed and standardized to assure good quality control. As a result, it was best to specify a "recipe" for the concrete base on a backlog of experience. Today, however, thanks to the work of the ACI, ASTM, CSI, and other groups, testing procedures that are dependable and accurate are available. The result has been a continued improvement of the coefficient of variation and achievement of reliable means of checking on quality and uniformity. Strength specifications enthusiasts point out that concrete producers are encouraged to improve their product when concrete is specified in this manner- at least on projects where the concrete undergoes testing. Bag concrete specificers note that no such control is exercised on jobs- such as most housing projects- where the concrete is not tested for strength, workability; or air content.