Processing solutions is checked by using:

Frequently processing solutions are replaced, which depends primarily on the rate of use of the solutions but also on the size of tanks, whether a cover is used, and based on the temperature of the solutions. In most offices, the solutions should be changed weekly or every other week. The results of the step-wedge test help determine the proper frequency. A simple procedure can help determine when solutions should be changed. A double film packet is exposed on one projection for the first patient radiographed after new solutions have been prepared. One film is placed in the patient’s chart, and the other is mounted on a corner of a viewbox in the darkroom. As successive films are processed, they are compared with this reference film. Loss of image contrast and density become evident as the solutions deteriorate, indicating when it is time to change them. The fixer is changed when the developer is changed. Key Concept: Processing solution may be checked by using a reference radiograph or a step wedge phantom or a normalising device. Karjodkar second edition