I have only ever set my watch to the closest minute, never feeling the need to get those pesky seconds correct. The clock on my phone doesn’t even give seconds, so, without a watch, I’m not even losing any degree of accuracy. You don’t have to manually set a smart phone’s time, and I’ve always assumed that modern smartphone time was accurate.
My current wristwatch is the popular Casio W800HG, which promising a ten year battery life, a light up display, and water resistance up to 100m. Amazon reviewer “onwa” (verified purchase) reports that, on average, time on the watch drifts by a little more than a second each week. Is that good?
For most of my day to day activity this degree of accuracy is perfectly good. In my work, we deal with time to the tenth of a millisecond when looking at latency of an internet connection, so by this standard it would very poor. Looking back into history, for George Harrison — inventor of the first marine chronometer — and generations of seafarers, that difference is worth 0.25 degrees of longitude. A degree of longitude is the equivalent of sixty nautical miles at the equator, so after a months sailing you might be out by quite some distance in your tracking, and possibly out of pocket. Losing a degree of longitude would have put John Harrison you out of the running for even third place prize set in the Longitude Act (1714) by the British government.
Latitude, by Dava Sobel, is the story of the creation of accurate clocks. That is to say accurate in all possible conditions. A maritime chronometer, as they became known, needs to be accurate when exposed to changing temperatures, pressures, movement, and even variation in gravity itself that such a device can expect to be exposed to when sailing the globe. While latitude could be easily computed with a sextant and the sun at noon, longitude is far more difficult. There were essentially two candidate strategies. The first was to develop a more sophisticated system of astronomical observations. The second was to build the reliable maritime chronometer. The first option appealed to those who enjoyed astronomy (and there were many indeed in the 17th and 18th centuries), the second would be far simpler and appeal to the sailors who would use them.
John Harrison was the “Lone Genius” horologist who rose to the challenge. Most of Sobel’s books is devoted to his life, his clocks, his genius, and most of all his difficulty claiming the longitude prize, even as his clocks won over the sailors who navigated by them. In part, this was due to Harrison’s own perfectionism, and partly this was due to Big Astronomy’s certainty that clocks could not be the right solution when the stars were surely the most reliable guides.
Longitude seems to believe that the reader will be hooked on the injustices Harrison suffered in trying to claim the prize that was rightfully his. Who doesn’t enjoy a frustrated genius? But Longitude is at it’s best when it manages to get away from this tired narrative arc. I like personalities as much as the next man or woman, but the petty squabbles just read as tiresome. There is so much richer material here. The chapter devoted to describing the world before ready access to latitude alone is captivating. Then there are actual challenges involved in making a reliable chronometer, which I will generously assume involves so much of interest — history, science, and culture — that Sobel is simply preventing it taking over the book completely. Then there is the subsequent popularization of reliable pocketwatches as craftsmen developed the means to start producing them, if not in mass, at least in serious numbers. This discussion, which comes at the end, begs the question of how we get from there, to here, and the clock on my smart phone.
The state of the art in timekeeping is the atomic clock, which uses the quivering, shivering idiosyncrasies of physics at the molecular level to keep track of the seconds. International Atomic Time is kept by over 450 of these clocks distributed across 80 national laboratories. My phone plays its own version of What’s The Time, Mr Wolf with these atomic clocks, getting sporadic updates to maintain its own pizoelectric crystal. But while an atomic clock can be accurate to 10^-16 seconds, time.gov tells me that my phone is 1.889s out. In nautical terms, that could be a shipwreck.