In this phase and in phase 4 validation of all examinations and equipment is necessary. Therefore, an SOP should be written for this activity.
Validation is the evaluation of whether a procedure or a piece of equipment actually delivers the values you are expecting to receive. For example, an incorrectly manufactured spectrophotometer could have been delivered to the laboratory, i.e. instead of a 600 nanometer filter a 400 nanometer filter was installed. When this spectrophotometer is set at measuring samples at a wavelength of 600 nanometers, it gives a value as you measure samples. But only when you compare the value from the new spectrophotometer with that from an old spectrophotometer you see that this value is different. This will lead you to finding that the filter for the 600 nanometer setting is wrong. The process of comparing the values from the new spectrophotometer with those from the old one is called validation.
Make sure that this SOP is read by all relevant personnel members.