Camera time versus real time

From GPSBabel

If you’re using your GPS and one of the applications that geotags photos based on a GPS track log you’ll have realised that it’s crucial to have the camera’s clock set correctly - otherwise the image locations will be shifted. If you’re lucky the software you’re using will allow you to specify the time difference between the camera’s clock and real (GPS) time. Here’s a tip for working out exactly what the camera’s time error is.

Find an accurate clock - the one in your GPS is good - or use your computer clock if it’s set to internet time.

Now

• set the clock to display hours, minutes and seconds and
• take a picture of it with the camera.

So if you're using the clock on your GPS take a picture of the GPS display. If you're using the clock on your computer take a picture of the screen.

You’ll end up with something like this:

So now you have two times: the time the camera thought it was and the accurate real world time when the picture was taken.

Subtract the camera time (from the image info) from the real time (the time shown in the picture you took) and use the result to set the time offset in your geotagging software.

In this case the camera thought it was 22:19:46 and the real world thought it was 23:19:27 so the error is 1 hour minus 19 seconds - or 3581 seconds.