Between seconds one and sixteen inclusive past the minute, the current difference between UTC and UT1 is transmitted by doubling some of the once-per-second ticks, transmitting a second tick 100 ms after the first. (The second tick preempts other transmissions, but does not get a silent zone.) The absolute value of this difference, in tenths of a second, is determined by the number of doubled ticks. The sign is determined by the position; if the doubled ticks begin at second one, UT1 is ahead of UTC; if they begin at second nine, UT1 is behind UTC.