How are reference developing times determined?

Question

For developing there is tons of information out there for many combinations of film and developer, often at multiple dilutions, temperatures and ISO settings. Ilford for example has development times for its various developers and films in their manuals, and even some films of other vendors. The Massive Dev Chart has an immense collection of combinations.

So how exactly are these established? Is there some procedure? Say, shooting a reference image at various ISO settings and then making measurements of highlights, shadows, contrast and grain? Or is it a much more subjective process where trial-and-error is applied and the end results interpreted by experienced people? Would a producer of film and/or developer such as Ilford or Kodak use different means than people contributing to the Massive Dev Chart?

Answer 1

It is closely related to the determination of B&W film speed, which is specified in the standards ISO 6 and ISO 2240 and based on sensiometric density and contrast measurements of the negative. The actual speed of a black and white film can only be measured after it has been developed and the reference development times are defined, so that the negative matches the film's box speed in combination with these development instructions.

A summary of the method can be found on Wikipedia:

Film speed is found from a plot of optical density vs. log of exposure for the film, known as the D–log H curve or Hurter–Driffield curve. There typically are five regions in the curve: the base + fog, the toe, the linear region, the shoulder, and the overexposed region. For black-and-white negative film, the "speed point" m is the point on the curve where density exceeds the base + fog density by 0.1 when the negative is developed so that a point n where the log of exposure is 1.3 units greater than the exposure at point m has a density 0.8 greater than the density at point m. The exposure Hm, in lux-s, is that for point m when the specified contrast condition is satisfied.