https://developers.google.com/time/smear watch * Public NTP [ ] [Language ] Home Guides watch * Public NTP * Home * Guides * Configuring Clients * How to Get Help * FAQ * Leap Smear Details * Privacy * Home * Products * Public NTP * Guides [{ "type": "thumb-down", "id": "missingTheInformationINeed", "label":"Missing the information I need" },{ "type": "thumb-down", "id": "tooComplicatedTooManySteps", "label":"Too complicated / too many steps" },{ "type": "thumb-down", "id": "outOfDate", "label":"Out of date" },{ "type": "thumb-down", "id": "samplesCodeIssue", "label":"Samples/Code issue" },{ "type": "thumb-down", "id": "otherDown", "label":"Other" }] [{ "type": "thumb-up", "id": "easyToUnderstand", "label":"Easy to understand" },{ "type": "thumb-up", "id": "solvedMyProblem", "label":"Solved my problem" },{ "type": "thumb-up", "id": "otherUp", "label":"Other" }] Leap Smear Since 2008, instead of applying leap seconds to our servers using clock steps, we have "smeared" the extra second across the hours before and after each leap. The leap smear applies to all Google services, including all our APIs. Our proposed standard smear Many organizations use smeared clocks, and it would be helpful if the smears were the same. After all, the purpose of clocks is to read the same time in different places. We encourage anyone smearing leap seconds to use a 24-hour linear smear from noon to noon UTC. This smear combines the features that experience has shown to work well for many distributed computing applications: * The long duration keeps the frequency change small. The change for the smear is about 11.6 ppm. This is within the manufacturing and thermal errors of most machines' quartz oscillators, and well under NTP's 500 ppm maximum slew rate. * Centering the smear on the leap second, instead of having it begin or end at the leap second, minimizes the maximum offset. * Compared to a cosine smear, the linear smear is simpler, easier to calculate, and minimizes the maximum frequency change. * The 24-hour duration has been widely adopted by others implementing smears. We previously used a 20-hour smear duration, but changed to align with this more popular noon-to-noon interval. We plan to use this smear for all future leap seconds. Amazon uses this smear in AWS. One way to use it in your systems is to configure them to use Google Public NTP. Example of the standard smear In this example, we will suppose there is a leap second at the end of December 2021, although the actual schedule has not yet been announced. The smear period starts at 2021-12-31 12:00:00 UTC and continues through 2022-01-01 12:00:00 UTC. Before and after this period, smeared clocks and time service agree with clocks that apply leap seconds. During the smear, clocks run slightly slower than usual. Each second of time in the smeared timescale is about 11.6 ms longer than an SI second as realized in Terrestrial Time. At the beginning of the leap second, smeared time is just under 0.5 s behind UTC. UTC inserts an additional second, while smeared time continues uninterrupted. This causes smeared time to become just under 0.5 s ahead of UTC when the leap second ends. By continuing to run the clocks at the same slowed rate, the ongoing smear reduces this offset over the next twelve hours. By 12:00:00, smeared and leaping clocks agree again. TAI Unsmeared UTC Smeared time 2021-12-31 2021-12-31 2021-12-31 12:00:36.000000 11:59:59.000000 11:59:59.000000 2021-12-31 2021-12-31 2021-12-31 12:00:37.000000 12:00:00.000000 12:00:00.000000 2021-12-31 2021-12-31 2021-12-31 12:00:38.000011 12:00:01.000011 12:00:01.000000 2022-01-01 2021-12-31 2021-12-31 00:00:35.499976 23:59:58.499976 23:59:58.000000 2022-01-01 2021-12-31 2021-12-31 00:00:36.499988 23:59:59.499988 23:59:59.000000 2022-01-01 2021-12-31 2021-12-31 00:00:37.000000 23:59:60.000000 23:59:59.500005 2022-01-01 2021-12-31 2022-01-01 00:00:37.500000 23:59:60.500000 00:00:00.000000 2022-01-01 2022-01-01 2022-01-01 00:00:38.000000 00:00:00.000000 00:00:00.499994 2022-01-01 2022-01-01 2022-01-01 00:00:38.500011 00:00:00.500011 00:00:01.000000 2022-01-01 2022-01-01 2022-01-01 00:00:39.500023 00:00:01.500023 00:00:02.000000 2022-01-01 2022-01-01 2022-01-01 12:00:36.999988 11:59:58.999988 11:59:59.000000 2022-01-01 2022-01-01 2022-01-01 12:00:38.000000 12:00:00.000000 12:00:00.000000 2022-01-01 2022-01-01 2022-01-01 12:00:39.000000 12:00:01.000000 12:00:01.000000 Over the 86,401 SI seconds of the smear, the stretch in the 86,400 indicated seconds adds up to the one additional SI second required by the leap. A negative leap second, if one were ever to occur, would be smeared by speeding up clocks over the 86,399 SI seconds from noon to noon. Other smears Several other smears have been proposed or implemented. * UTC-SLS is a linear smear over 1,000 s before the leap (23:43:20 to 00:00:00). * Google's 2008 smear was a 20-hour cosine smear before the leap (04:00:00 to 00:00:00). This was the only time we used a cosine smear. * Google's second leap smear was a 20-hour linear smear centered on the leap. We used this in 2012, 2015, and 2016. * Bloomberg's smear is a linear smear over 2,000 s after the leap (00:00:00 to 00:33:20). * Meinberg has implemented a cosine smear of configurable duration. Software support for the smear Our open source unsmear library will convert in either direction between smeared time and unsmeared TAI or GPST. [{ "type": "thumb-down", "id": "missingTheInformationINeed", "label":"Missing the information I need" },{ "type": "thumb-down", "id": "tooComplicatedTooManySteps", "label":"Too complicated / too many steps" },{ "type": "thumb-down", "id": "outOfDate", "label":"Out of date" },{ "type": "thumb-down", "id": "samplesCodeIssue", "label":"Samples/Code issue" },{ "type": "thumb-down", "id": "otherDown", "label":"Other" }] [{ "type": "thumb-up", "id": "easyToUnderstand", "label":"Easy to understand" },{ "type": "thumb-up", "id": "solvedMyProblem", "label":"Solved my problem" },{ "type": "thumb-up", "id": "otherUp", "label":"Other" }] Except as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 4.0 License, and code samples are licensed under the Apache 2.0 License. For details, see the Google Developers Site Policies. Java is a registered trademark of Oracle and/or its affiliates. Last updated 2021-04-27 UTC. * User Forum User Forum Discuss Google Public NTP issues * announcement Announcements Subscribe to our announcements * Connect + Blog + Facebook + Medium + Twitter + YouTube * Programs + Women Techmakers + Google Developer Groups + Google Developers Experts + Accelerators + Developer Student Clubs * Developer consoles + Google API Console + Google Cloud Platform Console + Google Play Console + Firebase Console + Actions on Google Console + Cast SDK Developer Console + Chrome Web Store Dashboard Google Developers * Android * Chrome * Firebase * Google Cloud Platform * All products * Terms * Privacy * Sign up for the Google Developers newsletter Subscribe [Language ]