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Calibration

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3	3	Unless you are lucky, your voice recorder's clock is not as accurate as the atomic clocks used by the Global Positioning System. Therefore you need to be sure your recorder is accurate enough, and if it isn't to measure the difference and tell JOSM what that difference is. This process is called 'calibration'.
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	5	An error of 5 seconds per hour could mean you are 100m or more out after four hours surveying on a bike, and more in a car, if you are relying on the clock in the audio device to indicate position on a GPS track.
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5	7	To calibrate, you need to enter a number close to but not exactly 1.0 in the calibration setting of JOSM's [wiki:Help/Preferences/Audio Audio Preferences]. This number is the ratio of the sound recorder clock's notion of how long a recording is to the accurate time. For example, if the audio recording of a 3 hour interval turns out to be 3 hours and 15 seconds long, your calibration number is (3 x 60 x 60 + 15)/(3 x 60 x 60), which works out at 1.00139 (five decimal places is ample). If your recorder's clock runs fast, the number will be slightly less than 1.0. If it is very much different from 1.0, throw away your voice recorder!