A step-wedge phantom is used to assess the quality
assurance of:
How frequently processing solutions are replaced depends primarily on the rate of use of the solutions but also on the size of tanks, whether a cover is used, and 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.
Reference: White and Pharoah's Oral Radiology Principles and Interpretation 7th edition page no 251
Dark room
Timer of the X-ray machine
Chemicals used for processing
Radiation leakage from X-ray unit