Artemis dragged himself the last few steps to the bomb, dropping to his knees beside it. He wiped ash from the read-out with his sleeve, then spent a while studying it, nodding along with the flickering of its digital timer.
The numbers of the timer were behaving seemingly erratically: jumping forward, slowing down and even backing up slightly. But Artemis knew that there would be a pattern in here somewhere. Magic was simply another form of energy, and energy conformed to certain rules. It was simply a matter of watching the timer and counting. It took a while longer than they could afford, but eventually Artemis spotted the repeat. He ran the numbers quickly in his head.
'I see it,' he shouted to Qwan, who was on his knees beside him. 'It's mainly forward. An hour per second for a count of forty, followed by a deceleration to thirty minutes per second for a count of eighteen, then a slight jump backwards in time, one minute per second back for a count of two. Then it repeats.'
Qwan smiled weakly. 'What was the first one again?'

The Lost Colony, Chapter 14