the time zone indicator bits) encode the time of the first minute after the event. In the event of an added leap second, a 0-bit is inserted during second 59, and the special missing bit is transmitted during the leap second itself, second 60. Although the time code only includes two digits of year, it is possible to deduce two bits of century using the day of week. There is still a 400-year ambiguity, as the Gregorian calendar repeats weeks every 400 years, but this is sufficient to determine which years ending in 00 are leap years. The time zone bits can be considered a binary-coded representation of the UTC offset. Z1 set indicates UTC+2, while Z2 indicates UTC+1. The phase modulation generally encodes the same data as the amplitude modulation, but differs for bits 59 through 14, inclusive. Bit 59 (no amplitude modulation) is phase-modulated as a 0-bit. Bits 0–9 are phase modulated as 1 bits, and bits 10–14 are phase modulated as 0 bits. The civil protection warnings and weather information is not included in the phase-modulated data. Reception area With a relatively high power of , the DCF77 transmissions can reliably be received in large parts of Europe, as far as from the transmitter in Mainflingen. Within this range the signal strength of the DCF77 signal as specified by the Physikalisch-Technische Bundesanstalt (PTB) is ≥ 100 µV/m. This signal strength assessment was made according to the reflection model with a reflection (one hop) on the ionospheric D-layer. As an example, reception with consumer grade clocks — assuming the employed radio clock can manage reception with ≈ 100 µV/m signal strength — is possible in Norway (Bodø), Russia (Moscow), Turkey (Istanbul), Gibraltar and Portugal (during night hours). Metal structures or interference caused by other electronic devices can cause reception problems within this range. At shorter distances the DCF77 signal strength is much higher. As an example, under from the transmitter in Mainflingen the expected signal strength of the ground wave is ≥ 1 mV/m. Depending on signal propagation and multiple reflections (hops) and local interference the DCF77 signal can sometimes be received further away (see tropospheric propagation). This is associated with a significant decrease in the signal strength and depends on many factors, e.g., the daytime and season, the angle of incidence of the skywave on the D-layer and the solar activity. Control The control signal is not