Setting the Macintosh Clock to
Coordinated Universal Time (UTC)

All seismometers worldwide are set to the Coordinated Universal Time (UTC) standard. This allows seismologists to have a synchronized and precise measure of time for recording and locating seismic events. In order to achieve this the stations on the Ohio Seismic Network use the Garmin GPS II+ hand-held receiver to get absolute time from the GPS satellites. Before setting up the Mac clock the GPS receiver needs to be connected to the computer, turned on, and configured properly. If this has not been done go to the Connecting the Garmin GPS II+ Receiver and Garmin GPS II+ Receiver Setup sections.

To set the Macintosh clock as 24 hour clock on Coordinated Universal Time (UTC) follow these instructions:

• Click and hold the mouse button on the "Apple Menu" icon (upper left on the Desktop).
• Scroll to "Control Panels."
• Scroll to "Date & Time", release mouse button.
• The "Date & Time" Control Panel should be open on the Desktop.
• Make sure the "Current Date" is correct.
• Click "Time Format."
• Click "24 Hr" button.
• Click "OK."
• Make sure all "Daylight-Savings Time" check boxes are blank.
• Click "Set Time Zone."
• Scroll to and click "London, England", should be high-lighted now.
• Click "OK."
• Click "Clock Options."
• Check the "Display the time with seconds" check box. All other check boxes should be blank.
• Click "OK."
• Turn on the GPS Receiver. After the initializes and collects data from the satellites go to the page which displays the time.
• Go back to the "Date & Time" which should still be open on the Desktop.
• Set the "Current Time" to read exactly the same as the time display on the GPS receiver.
   
  Note: The time has to be precisely set to the second. Any variation from the GPS clock will cause problems when starting up the GPSgraf and SeismoGraf Applications. The procedure that works best is to first set the hour and minute. Then, set the seconds about 15-30 seconds ahead of the GPS clock. The seconds should be high-lighted and frozen. Have someone count the seconds on the GPS clock. At the exact moment when the two clocks match click the mouse anywhere in the control panel. The Mac clock should be running now with no variation from the GPS clock.
• The Mac clock is now set to UTC format. Close the "Date & Time" Control Panel.