There were several different methods for developing negatives:

Inspection

This was the earliest and was still in use well into the 20th century. The negative was placed in a dish with the developing solution, the photographer judged when development was complete by holding the plate to a safelight. To compensate for wrong exposure or lack of contrast it was normal, at the time, for the constituents of the developer to be altered during development based on how the image was appearing.

Factorial

Introduced in 1893 by Alfred Watkins. It was found by Watkins that the time of initial appearance of the image indicated the speed at which the developer was working and that the complete development time was a simple multiple of the appearance time. The multiple differed for each developer and was known as the Watkins Factor. The type of plate and the temperature affected the appearance time but not the Factor. The photographer could alter the Factor depending on the degree of contrast required.

Stand

Very weak developer was used together with a prolonged development time of several hours. With shortened times this method merged into the Time method. A tank was generally used.

Time

Also called Time & Temperature. In the early 1900s development of plates and especially roll-films started to be standardised based on the type of developer, temperature and the type of plate. The popularity of roll-film, which was difficult to process by inspection, and smaller negative sizes were major factors in this change. The change meant that development could take place in light-tight tanks rather than a dish. With development (and enlarging) now able to take place in daylight, away from the darkroom, this branch of photography was opened up to the beginner and part-time photographer.

Thermo

In the early years of Time development the factors affecting development time (temperature, type of developer and plate type) were understood but not well formulated. Around 1908 Watkins, with his skill of systematising, published tables of plate types classified into their development speeds. A table was then used to give the dilution strength of developer to be used based on plate type and developer. This combination gave a solution that required a fixed time (6 ½ m for dish, 24 m for tank) at 60°F to produce a correctly developed plate. For other temperatures the Watkins Time Thermometer or tables supplied with the Watkins Time Developer could be used. The plate classification can be found on the Watkins speed list, plates were grouped into: VVQ, VQ, Q, MQ, MS, S, VS for very very quick, very quick, quick, medium quick, medium slow, slow, very slow. The standard Time Thermometer was calibrated for developers having a Temperature Coefficient of 1.9, for other developers the photographer would need to construct his own scale, a template was provided to do this. Watkins published and patented details on how to construct a calculator with settings for Temperature Coefficient and temperature but this does not seem to have been made commercially. Thermo became obsolete as better information was published by plate manufacturers. The Temperature Coefficient is the rate at which the development time changes with varying temperature, its value is expressed for a 10°C temperature change.

Daylight developing tanks, both plate and roll-film, for the Time method appeared in the early 1900s. They were preceded by what might be described as miniature darkrooms that could be operated in daylight, these took the form of an enclosed tray or developing area, a safelight window to inspect the plate and a spout to pour out the liquid.