You can check the color of the coffee perking in the perk knob. But in my experience, this hasn’t always been the most accurate. So, I set a timer after the first perk, and turn the stove off when the timer runs out. There usually isn’t a sign that your coffee is “done” percolating. If your coffee stops perking in the perk knob, it means that all the water has evaporated, and your camping percolator is boiling dry (which can be dangerous).