WHICH TIMER MODEL TO BUY - I OR - III?
You have noticed that all the timers with two or more functions are made in two models. The - I and the - III. The reason for this is to optimize the rotational speed of the shaft for the intended use. CAT I rules allow 5 minute DT times, which dictates that the timer clock run slow enough to allow the ten turn scroll to provide this much delay. This also impacts the number of degrees of turn you will get for your engine run time. In general, it is easier to set the engine time if the clock runs faster. So, we make two models of these timers. One for CAT I needing 5 minute DT, and one for CAT II and III needing 3 or 2 minutes.
If you will be flying under CAT II or III rules, you will be much happier with the - III model timer. It will make it easier to set the shorter engine run times associated with these events.
Just because the timer will do 5 minutes does not make it a better timer than a 3 minute one. They are the same, and we build them this way to accommodate our customers who want the timer optimized for they way they use it.