Impact of Too Little Weight
What makes a dead-beat escapement stop? One cause is too little driving weight. The previous plots are for a Viennese month runner with a 3.12 pound weight. If this mechanism were far enough out of beat it would not run with this weight. But, even if it is in beat - as in the tick is above the average half the time, and below the average half the time, as shown in the first beat plots - with too little weight (in this case, 2.44 pounds) the width of the pendulum swing will slowly decrease, and the duration of the tick and the tock will slowly digress until the mechanism stops. In this example, the mechanism stopped when the tick was around 0.83 and the tock was around 0.69. This also gives one an idea of how "out of beat" this mechanism can be before it will stop.
Which brings up another point – when I am putting a mechanism in beat I swing the pendlum just enough to get the mechanism ticking away. With minimal swing the unevenness of the beat is amplified – whereas the beat may sound totally even with a larger swing. By setting the clock in-beat with minimal swing you are giving the mechanism the best shot at running even if there are minor challenges in the gear train that result in variations in the force applied to the escape wheel.
Note – in this plot I did not have Excel draw a line between subsequent data points – which makes the plot look a little different, but still gives the same overall patterns.