The times given in this book are all based on the sun clock or a clock adjusted to solar time. It is advisable to have at least one clock on solar time in order to facilitate the control of one's sleeping times: Adjust a clock to Greenwich Mean Time (GMT, see right column). Next, in the case of plus "+" one sets the minute hand of a clock forward (clockwise) for the indicated amount of minutes, in the case of "-" the hand is moved backward. This will show local solar time. To the east of 0 degree longitude (Greenwich/London) clocks have to be put forward, to the west, back. For monitoring: 12 noon solar time is always when the sun is at its zenith! - When in doubt, seek the advice of local mathematicians, astronomers, etc.
Examples: In Rome the sun clock should be set forward 49 minutes with reference to Greenwich Mean Time (GMT), in Moscow 2 h. 30 m., in Tokyo 9 h. 19 m.; in New York the sun clock should be set back 4 h. 56 m., based on GMT.

Solar (local) time:
As the basis we avail ourselves of 0 degree longitude which runs through Greenwich near London: The adjustment of the solar clock proceeds as follows:
1) Set clock to Greenwich Mean Time (GMT):
a) During Winter (from last Sunday in Oct. til last Sunday in March): Set clock to public time in London/Great Britain = GMT.
b) During Summer (at "Daylight saving time", from last Sunday in March til last Sunday in October): Set the clock to public time in London/Great Britain and turn the clock back one hour: your clock will now show GMT. - For adjustment you can also use Central European time (MEZ, CET); but public time (= MEZ) in Paris, Berlin, Rome is always 1 hour ahead of public time in London.
For details:
2) The globe (360 corresponds to 24 hours) is divided into 180 east and 180 west longitude, 1 degree longitude therefore corresponds to exactly 4 minutes (12 hours = 720 minutes ./. 180). At one's place of residence the clock is put 4 minutes forward (+) per 1 degree of longitude (east of Greenwich) and 4 minutes back (-) per 1 if one is west of Greenwich.
Example: St. Petersburg is three hours ahead of GMT in Winter. Therefore the clock is put back three hours to GMT, during "Daylight saving time" in Summer yet another hour to get GMT.
St. Petersburg lies at 30 20' longitude east, so (60' = 1) the clock is put forward again 30,33 x 4 minutes = 121 minutes (and 32 seconds). Now we have St. Petersburg solar time, which determins our natural sleeping time!