In a method for power control in a telecommunication system, the transmit power is adjusted based on at least the mutual information expression or a representation thereof. A human must interpret an image to enter this universal text based secret. The electricity thus produced in a downhole environment is conducted to the surface where it can be used as an effective electrical source. A comparator circuit compares the GR signal with the N PR signals to provide N comparison output signals, the N comparison output signals indicating position and time that the GR reference signal moves across the ladder. The present invention allows accurate detection of an evoked response of the heart, to thereby determine whether each electrical stimulus results in capture.