The shutter timer error of a 60 Co unit was determined to be +2 seconds. If the treatment time was computed to be 58 seconds, what time must be set on the machine?

In this scenario, the shutter timer error indicates that the machine's timer runs longer than what is intended. Since the error is +2 seconds, it implies that if the machine is set to deliver a treatment time of 58 seconds, it will actually deliver 60 seconds due to this error.

To achieve the desired treatment time of 58 seconds, the operator needs to account for the +2 seconds error when setting the timer. Therefore, to ensure the actual delivered time matches the intended treatment time, the timer must be set to a total of 60 seconds. This compensates for the +2 seconds that the machine adds to the timer's setting.

Consequently, the time that must be set on the machine is 60 seconds to ensure that the patient receives the correct dose for the intended treatment duration.