I used the bottle cap because at the time it was the right size and handy but a knob is great. The adjustment is so much easier. Moving the thermostat just a hair can make a big difference. Good luck and have fun...I got a bottle cap & asked my hubby to attach it to the incubator for a knob & when I got home, he had used an actual knob! I'm calibrating it now & I'm so excited! I have the best hubby ever!!!
