The number of times that the DCF signal state is read. This is the number of times per second that the interrupt is executed. This value is calculated by the compiler. The highest possible timer pre scale value is used and the lowest possible number of times that the interrupt is executed. This gives least impact on your main application.
You can override the value by defining your own value. For example when you want to run some own code in the interrupt and need it to execute more often.