A watch running 15 seconds fast... per minute!

We published another service video, this time of a peculiarly running Vulcain alarm watch. The Vulcain Cricket 120 was launched in 1947 as the first alarm watch and quickly gained popularity. It became known as the "President's watch" as Truman, Eisenhower, Nixon, Johnson etc received a Cricket at their inaugurations and wore them with pride.

This particular watch doesn't run well and frequently stops. When it does run however, it runs 15 seconds fast per minute and the timegrapher labels it as having a 25200 bph movement while we know for a fact it should be 18000. What is up?