To simplify the application of the various empirically developed flow equations, specialized slide rules were developed. Most of these devices are designed for the use of one specific flow formula under a set of restricted operating conditions. Made of plastic, paper, metal, or wood, a circular format is often used to maximize precision by increasing the length of the scales while minimizing the overall size of the calculator. These devices are especially useful for the sizing of service lines and stub mains.
The Briggs Gas Flow Calculator incorporates "Dr. Pole's Formula", introduced to the gas industry in 1851. Despite the age of the calculation method, this calculator was widely used well into the 1960s for sizing small diameter, low pressure stub mains and services.
The yellow high-pressure and white low-pressure "Gasflo" calculators were marketed by Energy Commuications, Inc. in the 1970s and 1980s. The high-pressure calculator is based on the Weymouth and Cox formulas and was recommended for use in piping systems operating greater that 1.5 psig. The low-pressure calculator was based on the "a standard flow formula applicable to the flow of gas in piping at low pressure"; probably the low-pressure version of the Spitzglass formula. A unique feature of these calculators is that the parallel English and metric scales can be used interchangeably without having to convert from one to another.
As of April 2007 the high-pressure version is apparently still available from the Oildom Publishing Company of Texas.
The Bader flow calculator also uses the low-pressure version of the Spitzglass equation. These calculators are still widely used for service sizing. The example on the left is the generic version.
The second example (middle and right images) was customized for Bay State Gas and Northern Utilities with the addition of each company's logo and with directions for its use printed on the back of the calculator. Interestingly, the directions printed on the back are the same directions as found on the back of the Yankee Gas calculator described below, and are not consistent with the labels and scales on the front side.