Landis' formula does indicate 100% duty = 0v...
Duty Cycle = [1 - (V{pin 3}/V{max})] x 100%
http://www.landiss.com/mixture.htm
...1 more highly credible rumor...
There are some symbols (in my second sig link ...1st attachment) next to the 'lambda tester type' description that I don't understand the meaning of :
100% IR and 100% (?)---see link...
Anybody?