TOPIC 2 TIME-CONVERSION COMPUTATION
With U.S. naval ships and aircraft deployed throughout the world, time computation becomes a matter of concern to virtually every naval member. Communicators use ZULU time in messages and other record communications. It is extremely important that you know how to make time conversions from local to ZULU time and from ZULU to local time. Those involved in collection, processing and reporting, and traffic analysis must be able to make quick and accurate time conversions throughout their working day.
CONVERSION FROM LOCAL TIME TO ZULU TIME
We know the ZULU time zone has the numerical designator zero (0). At this point, the "+" or "-" assigned to each of the other zones comes into play. To convert the local time to ZULU time, simply add or subtract as indicated by the sign (+ or -) of the local time zone.
For example, we are in Pensacola, Florida, and wish to assign a date-time group (DTG) to a message. We will have to use ZULU time for the message. Pensacola is in the SIERRA time zone and is designated +6. The local date and time is 1910455 (the 19th of the month at 10:45 A.M.). Since the SIERRA time zone is +6 (Pensacola local time), add 6 to the local time of 1045. Our answer is the conversion of 1910455 to ZULU time 191645Z.
Our problem looks like this:
1910455 (local DTG)
+6 (Pensacola is in zone +6)
191645Z (ZULU DTG)
NOTE: Remember, the +6 must be placed under the "hours" of the local DTG.
RULE: FROM LOCAL TIME TO ZULU TIME-APPLY THE SIGN.
To check ourselves for complete understanding, let's take one more example of converting local time to ZULU time. This time we are in Kamiseya, Japan, and wish to assign a DTG to an outgoing message. First, we have to know the zone designation for Kamiseya-INDIA (-9). The date and time in Kamiseya is 1018001. Using our formula, we apply the "-" sign and subtract the local zone (9) from the local time:
1018001 (local DTG)
- 9 (Kamiseya is in zone -9)
100900Z (ZULU DTG)
These examples can help you convert local time to ZULU time from any place in the world. The only variations that you will encounter involve the International Date Line and daylight saving time (DST), each of which will be treated separately later.