- What it is
- A system clock whose date, time and time zone you have looked at recently and found to be what you expected.
- How you get one
- You look at it. If it disagrees with a source you believe, you correct it and note that you did.
- Where to keep it
- Running on whatever hardware you sit at, with automatic syncing left switched on unless you have a considered reason otherwise.
- How it goes wrong
- It drifts, or a dead battery resets it, or a time zone changes underneath you and only the displayed hour moves.
- What fails without it
- Certificate validity checks and signature timestamps stop behaving sensibly, and your own dated notes become fiction.
- Time to acquire
- Seconds to look. Slightly longer if the answer is wrong and you have to work out why.
The item is the glance
Listing a clock as something you possess sounds odd until you notice how the failures happen. Nobody lacks a clock. What people lack is any recent moment where they looked at one and confirmed it. The clock is issued with the machine. The confirmation is the thing you have to supply, and it decays, which is why this entry is tagged as going stale.
Treat it as a small act with a date attached. Looked at it on Sunday, it was right. That sentence is the artifact. Assuming it is right because the machine came from a shop is not.
What a wrong clock touches
Three areas, and none of them announce the cause when they break.
- Certificate validity. Certificates carry a window of dates. A machine that thinks it is a year out will judge that window incorrectly and will either complain about something fine or accept something it should not.
- Signature timestamps. When a signature carries a time, that time is checked against yours. A large disagreement makes the result meaningless, and the message you get back rarely says the word clock.
- Your own records. Every dated note in this inventory takes its date from the machine. A clock that is out puts the wrong day on your address file and on anything you write about an order.
The third one is the quietest and the most annoying to unpick. You end up with a set of notes whose relative order is right and whose absolute dates are all shifted, and you will not notice until you try to compare them against something external.
Machines that lose time
Some machines are worse offenders than others and it is usually predictable. A laptop that spends weeks switched off. An old desktop with a battery nobody has replaced. A machine that boots between operating systems and where the two disagree about what the hardware clock means. Anything set up while travelling, where the zone was picked by whatever network it happened to be on.
If your machine is in one of those categories, the glance is worth making a habit rather than an occasional impulse. If it is a phone or a laptop that is online most days, the automatic sync usually holds and the check takes a second, which is a poor excuse for skipping it.
Zone and date, not just the hour
People check the time on screen and stop there, because the hour is the visible part. The hour being right does not mean much on its own. A machine can show a plausible hour while sitting in the wrong zone, and a machine can show a perfectly good time on entirely the wrong date after a reset.
So look at all three. Date, time, zone. It takes no longer than looking at one of them, and the date is the field most likely to be quietly wrong on a machine that has been off for a while.
Fitting the check somewhere it will happen
A check nobody performs is not an item. Attach it to something you already do rather than inventing a ritual. Opening the browser is a reasonable hook, since the clock matters most from that point on. Sitting down to write in whatever you write on is another, because that is where a wrong date does lasting damage.
The wider habit of dating things is covered in the reference notes on dates. This entry is the precondition for all of it. A date is only worth writing if the machine supplying it has been looked at.
Questions that come up
My clock is off by a few minutes. Does that matter?
Minutes are unlikely to cause the failures described here, since the windows involved are usually far wider than that. Hours, days and years are the sizes that break things, and those come from resets and zone mistakes rather than from drift. A few minutes out is mostly a sign that syncing is working, since a machine with no sync at all tends to wander much further than that.
Should I turn off automatic time syncing?
For almost everyone, no. Syncing keeps the clock in a range where the checks that depend on it behave sensibly, and turning it off replaces a small automatic process with a manual one you will forget. Anyone with a specific reason to disable it already knows what that reason is and has accepted the maintenance that comes with the decision.