A web site dedicated to precise Time & Frequency
...one man's quest for the most accurate clock...


Twenty years ago I wanted to build a LED digital analog clock that would be accurate to better than one second per year -- so I would have the fun of adjusting it when a leap second occurred.

This simple goal resulted in a most interesting journey into electronics, horology, astronomy, test equipment, quartz oscillators, rubidium and cesium atomic clocks, hydrogen masers, frequency counters and phase comparators, GPS, Loran C, GOES, and WWV / WWVB radio receivers. That makes me one of the Time-Nuts.

By now I've exceeded that goal by a factor of a million: the best clocks in my collection (active hydrogen masers) are accurate to better than one microsecond per year. Excluding national government laboratories, my home time lab now has the most accurate clock in the world.

Perhaps you've heard: A man with one clock knows what time it is. A man with two clocks is never sure. But I would add further: A man with three clocks is more sure than a man with two clocks. And so the clock collection started...


Project GREAT 2016a: Hawking, Einstein and Time dilation on Mt Lemmon - for GENIUS by Stephen Hawking PBS TV show New!
Nixie Tube UTC clock - including Leap Second countdown clock Updated!
How to Watch a Leap Second - on December 31, 2005
Extreme Amateur Timekeeping: From Harrison to Einstein - NAWCC Time for Everyone Symposium New!
Project GREAT - General Relativity Einstein / Essen Anniversary Test
3 kids, 3 cesium clocks, a family road trip to measure relativistic time dilation
A close look at Clock B - in search of the best open-air pendulum clock Updated!
Precision Pendulum Clocks, Gravity and Tides - in search of the best pendulum clock
La Crosse 1235UA UltrAtomic Radio Controlled WWVB wall Clock - ultra-atomic, enhanced WWVB New!
Nixie Tube iPod Clock - a small virtual Nixie clock Cool!
Most Accurate Wristwatch - the first atomic wristwatch
Clock Powers of Ten - from the worst to the best clock in decades New!
Climbing With Atomic Clocks - there's a better way
Atomic Nixie tube clock - the most accurate Nixie clock
Lunar Eclipse photos - October 27th, 2004
Transit of Venus photos - June 8th, 2004
Museum of HP Clocks - precise time from HP 100A to 5071A New!
BNC Chess - what to do with extra RF connectors
The license plates - fun over the years
TAI, UTC, GPS clocks - with links to time scales and leap seconds
MJD & GPS Calendar - Modified Julian Dates and GPS Week Numbers
WildBlue - plots of satellite internet performance
9.192,631,770 GHz - see cesium atomic resonance
New Years 2001 - cesium rollover
GeoWriting - writing large words with GPS track logs
No Earthquake damage today - 28-Feb-2001
New Years 2000 at NIST - where were you for Y2K?
GOES Time and Frequency Receivers - time from space
A "house" standard - space for time
Why LeapSecond.com? - time and space
Reduction in GPS timing error when SA was turned off
Hydrogen Maser auto-tuning value - live webcam
Some photos of the old lab - photos of new lab coming soon
Sulzer 2.5c quartz oscillator - stability better than 3 x 10-13
Z3801A Quartz Oscillator Comparison - all good but not equal
Z3801A EFC Resolution Calculation - 5 x 10-13 per DAC unit
2002 20/02 20:02 - the triple palindrome minute
Allan Deviation of some of my frequency standards
Ultralink WWVB receiver "D" command - one bit per second
Ultralink WWVB receiver "T" command - 5 Hz samples
A measurement of 60 Hz mains power - how stable a timekeeper?
LeapHour.com - replace 3600 leap seconds with one leap hour New!
The State of the Art in Amateur Timekeeping - PTTI 2003 paper
The Time-Nuts mailing list - getting started with amateur time & frequency Updated!
Amateur Time Hackers Play With Atomic Clocks at Home - recent WIRED news article
Time Hackers Tinker With Their Atomic Toys - gallery of WIRED photos
Unobtanium Clock: So Accurate it converts Time to Money - April Fool's 2010
Louis Essen and Leap second history - a first hand report
Classic hp Hewlett-Packard Application Notes for GPS, Time and Frequency - PDF archive

Map of LeapSecond.com:

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