Final answer:
The standard speed setting for a 12-lead EKG on a patient with an accelerated junctional rhythm is 25 mm/sec, which allows for accurate waveform representation and interpretation.
Step-by-step explanation:
For an EKG technician performing a 12-lead EKG for a patient experiencing an accelerated junctional rhythm, the standard speed setting to use is 25 mm/sec. This setting is the industry standard for adult EKGs and is used to ensure that the waveforms are accurately represented and can be readily interpreted by clinicians. Adjusting the speed setting can distort the EKG tracing, leading to potential misinterpretation of the patient's heart rhythm.