We Got The Beat

Time: it's a funny thing. We can't measure it directly. The best we can do is construct mechanisms that have some kind of periodic behavior and then count the "beats" (as watchmakers call it) that they produce. There have been all kinds of sources of periodicity used during human history. The heart beat for short periods of time. The movement of the Sun across the sky for the day. The phases of the Moon for periods of a "moonth". The seasons for the year. There were many attempts to make time keeping devices - candles with marks drawn on them, water clocks that counted drips, sundials, hourglasses. But none of these were accurate enough to measure longitude, the angular east-west distance across the Earth. (Latitude can be determined by the height of the Sun above the horizon, taking the season and the hemisphere into account. There are almanacs still published today with the numbers you need to do this.) Navigators going all the way back at least to the ancient Greeks and Polynesians had known that timekeeping could be used to determine longitude, by comparing local time (e.g. local noon, determined by the sun) with a clock set to the time at the port from which you departed. But it wasn't until the mid-to-late 1700s that there was a "chronometer" design accurate, precise, stable, and reliable enough to carry on board ship that navigators were able to use it to determine their longitude. All "modern" clocks, from those initial chronometers until today, consist of an oscillator - a source of stable precise beats - and a counter - the watch face. And all oscillators are made of three basic components: a resonator (a source of periodicity derived from nature), a power source (a falling weight, a spring, a battery, the mains), and a feedback loop (known as an "escapement" in a mechanical clock). Many things have been used as resonators over the centuries (and all of these are still used today): a pendulum, a balance wheel, a quartz crystal, an atom of cesium, rubidium, aluminum, ytterbium. But no matter how sophisticated clocks become, they still have the three components that can be classified as a resonator, a power source, and a feedback loop. The clock below - on display at NIST in Boulder Colorado and whose photograph I took in 2018 - was sold by IBM in 1956. It is an electric pendulum "Type 37" clock that set itself from the NIST WWV/WWVH telegraphic time code using a vacuum tube radio receiver. It was typically used in factories as the master clock from which all other clocks were set.

NIST Time and Frequency Seminar 2025

Once again I attended the fire hose of information that is the U.S. National Institute of Standards and Technology (NIST) Time and Frequency Seminar. This three day, typically annual, event, held at their Boulder Colorado laboratories (commuting distance for me), covered such wide ranging topics as optical atomic clocks, practical measurement techniques for time and frequency, how to characterize and analyze frequency and phase errors in data, ways in which television and radio broadcasters might augment GPS for timing and positioning, and much more.

In honor of the event I wore my Rolex Milgauss. Felt cute, might delete later.

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My understanding is that virtually all national time and frequency metrology laboratories, including NIST (civilian) and the USNO (military) in the U.S., use an ensemble of cesium beam atomic clocks and hydrogen maser atomic clocks, the average of which is used to determine their contribution to the measurement of the SI second and the international definition of UTC. These are commercial devices, not laboratory experiments, and aren't astronomically expensive.

They use a combination of both because, even though the cesium resonant frequency is the (current) definition of the second in the international system of units, cesium atomic clocks suffer from jitter (short term variation), while hydrogen masers are more stable. The jitter in commercial atomic clocks is well understood, and the difference between a rack-mounted commercial cesium beam clock and a much larger and far far more expensive cesium fountain atomic clock in labs at places like NIST is all the extra hardware to try to reduce that jitter.

The image below is of the NIST F-3 cesium fountain clock. The collection of commercial cesium beam standards are kept locked up in another room.

Here's the thing: all hydrogen maser clocks suffer from drift (long term variation). And they all drift by a different amount. And it is not understood why. One hypothesis is it's some mechanism of aging of the components. If the manufacturers could eliminate this, they certainly would (and charge more).

The image below is of a decommissioned commercial hydrogen maser clock that I saw at NIST in 2018. You can't typically find one of these at NIST where it can be photographed because the running ones are kept locked in temperature controlled chambers adapted from commercial egg incubators.

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The blinking 1Hz LEDs in this brief video clip literally represent the real-time manufacture of the UTC(NIST) time scale (the U.S. civilian time base) and the U.S. contribution to the international determination of UTC.

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Next to the toe of my shoe is a survey marker embedded in the floor of one of the NIST labs. Atomic clocks are so precise now that centimeter changes in altitude have to be adjusted for, thanks to general relativistic effects.

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This was my fourth (2018, 2023, 2024, and 2025) and probably last time attending the Time and Frequency Seminar. It is so popular that not only does it sell out, but the waiting list is lengthy too. Could be time to let someone else become a certified Time Lord.

AgTech

It was World War II that permanently took my parents out of the agricultural (or maybe the vice) industry in rural eastern Kentucky where they grew up in families that were tobacco farmers and "distillers" (really): my dad joined the Navy, deployed on the U.S.S. Yorktown in the Pacific theatre, and my mom was literally a riveter at a defense plant in Columbus Ohio. Maybe it was the old family businesses that left me with a latent interest in the "ag" industry. Last week I attended another of the Colorado Technology Association's Insights Series: "Innovations in AgTech: How Technology is Shaping Colorado Agriculture". It was a terrific learning experience.

There were two keynote speakers, one from CoBank and the other from American AgCredit. These are cooperative banks that are part of the member-owned - like a credit union - Farm Credit System, a government-sponsored enterprise established by Congress in 1916 to insure farmers had access to loans. Why are these guys talking to an org like the CTA? Because by law they can only lend money to farmers; they can't lend money to agricultural technology startups trying to develop new technology for farmers, who are often running US$10Ms+ businesses with huge capital investments managed only using spreadsheets. 

So the banks find themselves trying to put venture capitalists together with AgTech startups to solve the problems their members have. Technology is a big deal in agriculture because labor is a huge cost. (Remarkably, land is another big cost, and many of the efficiency drivers provided by technology only scale with more land; a modern tractor can mow 175 acres of hay in four hours, and costs as much as a house.)

The event included a panel discussion with the two bankers (one of whom was formerly a rancher himself - he showed a photograph of him wrestling a steer to the ground), three former founders of successful AgTech startups, and a really interesting faculty member at Colorado State University - a land-grant university that was formerly Colorado Agricultural College - who is the Director of Ag Innovation at CSU.  (I learned that agriculture in Colorado, where I call home, is pretty unique in that the state has many different biomes, so that it lends itself to growing different crops and livestock, unlike, say, states in the Midwest.)

My work with Differential GNSS and Inertial Measurement Units, which I've written about here previously, was inspired by my interest in precision agriculture, used in applications like auto-steer for tractors, a technology which has led to a huge cost savings for farmers.

It's events like this that keep me renewing my membership in the CTA, a professional society I've been a member of since 2018. I'm not there to hire, to find work, to buy, or to sell; mostly just there to learn and to get ideas for my own projects. Although I routinely attend networking events like their upcoming C-Level at Mile High that are relatively expensive to attend, I do so mostly to support the organization, and because, in the case of C-Level, its fun to wander around on the party floor of Empower Field, a part of the Bronco's football stadium fans rarely if ever see. Also, the food is not bad. But when people choose to chat with me, I feel kind of guilty that I'm probably wasting their time. (I admit left the AgTech event as soon as it transitioned to the networking stage.)