Why is the Exact Time important?
There are 1440 (24 x 60) minutes in a day while the Earth rotates 360°. That means the Earth rotates 0.25 degree/minute. The field of view of a 26 mm eyepiece on ETX-90EC is 1.1 degrees. If the telescope is not tracking the target object, it will go out of view in 4.4 (1.1/0.25) minutes.

Every one minute of error in the Autostar's time, the target object will be off by seconds or 0.25°. If the time is off by 4 minutes, the target object will be off by 1°. Needless to say, if you do not set the Autostar's time to the exact time, the telescope will not point to the exact location of your target object either. Remember, a half of a degree off here, a quarter of a degree off there, and you will miss the target. Your Polar alignment and Alt/Az alignment with affected.

Your DC3-updated PC System Time

DC3 is a freeware utility program that will synchronize your PC system time an atomic clock server to hundredth of a second. See Precision Time Source.

Radio Digital Atomic clock
NIST (National Institute of Standards and Technology) radio station WWVB continuously broadcasts time and frequency information on its 60 kHz carrier frequency from Fort Collins, Colorado. WWVB provides coverage to the United States, Mexico, and Canada. The WWVB time code provides a convenient reference for many consumer electronic products such as desk clocks, wall clocks, and wristwatches.

Radio digital atomic clock receives a special radio signal up to four times per day to ensure accurate time within a nanosecond. Radio digital atomic clocks are not expensive, priced at about $40.00. Some of the radio digital atomic clocks even come with a thermometer. These atomic clocks are about the size of a pack of cigarettes.

Synchronizing Your Digital Watch with Computer Time
Your computer should now be updated with DC3. You may want to synchronize you digital watch with the computer time. Since different digital watches work differently, I will just use my Casio digital watch as an example. In my case, I bring up the PC clock and set my digital watch to about 30 seconds ahead of the PC time. My watch allows me to set the seconds to "00". Let's say the PC time is 6:32:30, I would set my digital watch to 6:33:00, when PC time reaches 6:33:00, I release the button on my digital watch. My digital watch is now synchronized with the very accurate PC time. I therefore always set my watch before I start my star gazing session if I'm not using my computer.

Different digital watches work differently; please refer to your digital watch's manual.