Perfect timekeeping is something that man will never attain by an instrument of his own making.  The only truly accurate time can be taken from the stars. Even the earth has been known to be a trifle behind time, and so has the moon. These variations, however, have not been set by timekeeping instruments but by the stars themselves as observed by man.

The precision clocks in the Unites States Naval Observatory and the Master Clock at the Hamilton Watch Company come as close to perfection in timekeeping as any instrument built today (1931).  These clocks are placed on concrete pedestals whose bases are in no way connected to the building which houses the instruments.  The bases are placed on separate foundations sunk deeply into the ground and thus guarded against vibrations taking place in the building itself which would cause time variations. The clocks are sealed in air-tight chambers and all operate in a temperature that is constant and unvarying.  The sway of the pendulum is regulated by the friction of the remaining air.  The air of the chambers is either pumped out or added to, and in this manner the clocks are adjusted.  The air friction on the pendulum is the adjusting factor.  With all these safeguards the clocks will not record time perfectly, but can be adjusted to within 1/100 of a second of accurate time a day.