Hamilton · Hamilton H-40

Hamilton Khaki Field King, Jazzmaster Day Date and Khaki Pilot Day Date power reserve: inside the H-40

The Hamilton Khaki Field King, the older Khaki King Auto, the Jazzmaster Day Date and the Khaki Aviation Pilot Day Date run on the H-40. It's a day-date automatic that runs for 80 hours, a little over three days, when fully wound.

Updated September 2026 · Based on manufacturer specs, published reviews and watchmaker/owner reports

Watches that use the Hamilton H-40

The H-40 is the day-date member of Hamilton's 80-hour movement family. If a current Hamilton shows both the day of the week and the date and has no chronograph, it's usually an H-40, though some day-date models use the closely related H-30. Always check the reference on Hamilton's site.

The H-40 is made by ETA exclusively for Hamilton. Tissot and Mido sell day-date versions of the same C07 family under their own names, but you won't find the H-40 name outside Hamilton.

Specs at a glance

History and where it came from

Hamilton introduced the H-10, H-30 and H-40 together in its 2014 collection, all with an 80-hour reserve. Worn & Wound's preview of that year's range lists the H-40 in the men's Flintridge, alongside the H-30 in the Pan-Europ and the H-10 in the Pilot Pioneer. The Khaki King, already Hamilton's day-date field watch, soon moved to the H-40 and became its best-known home.

The H-40 comes out of the same Swatch Group project that produced Tissot's Powermatic 80. ETA took its 4 Hz 2824 architecture, and in this case the 2834-2 day-date version of it, slowed the balance to 3 Hz, fitted a longer and thinner mainspring and reduced friction in the train. Reserve went from roughly 38 or 40 hours to 80.

Early H-40s were plain. aBlogtoWatch noted that the movement visible through the Khaki Field King's caseback wasn't decorated, a cost decision, and that the main visual difference from a generic ETA was Hamilton's engraved rotor. The 2026 Khaki Field King Day-Date adds a Nivachron balance spring, which Hamilton promotes for resisting magnetism and temperature swings.

Accuracy in the real world

Hamilton doesn't publish an accuracy spec for the H-40, and none of the Khaki King or Jazzmaster Day Date models is chronometer certified. Owner reports for the H-40 look much like the H-10: many see single-digit seconds a day, but there's more watch-to-watch variation than a spec sheet would suggest.

One owner's thread on the German Uhrenwerkstattforum is a useful reality check. Their H-40 ran about +15 seconds a day for its first five weeks, then drifted to around -20. The watchmakers replying said a steady -20 is easy to regulate and that doing so should be covered by warranty. The takeaway: if a new Khaki King runs well outside single digits, get it regulated under warranty rather than living with it.

The 3 Hz beat means the seconds hand steps six times a second rather than eight. It's slightly less smooth than an older 2834-based Khaki King, but you'll only notice side by side.

Reliability and servicing

The H-40 inherits the C07 family's good reputation, and there's no known systemic fault. The day-date works are the part to treat with a little care: day and date wheels add parts that can be damaged by setting at the wrong time of night.

Servicing follows the usual Swatch Group pattern. Hamilton's service network may swap the movement rather than overhaul it, and parts access for independent watchmakers is restricted. Some independents will still service it; ask before assuming. Many owners wear the watch until reserve or accuracy drops noticeably, rather than servicing on a fixed schedule.

Quirks worth knowing

• The day-date danger zone. Don't quickset the day or date while the calendar is changing over, roughly late evening to the early hours. Here's why.
• Setting the day. On most day-date movements you advance the day by turning the crown the opposite way from the date in the quickset position. If one direction doesn't move the day, try the other rather than forcing it.
• Plain finishing on older models. Earlier Khaki King and Field King casebacks show an undecorated movement with an engraved rotor. It's normal, not a sign of a cheaper movement.
• H-40 or H-30? Both are 80-hour day-date movements from the same family, used in different models. Hamilton's own reference page is the reliable way to tell which one a watch has.
• Slow to fill. From a stop, give it 30 to 40 crown turns before putting it on.

How it compares

• H-10. The same movement without the day wheel, found in the Khaki Field Auto and Jazzmaster Viewmatic. Same 80 hours, same behaviour.
• H-30. Hamilton's other 80-hour day-date calibre, in the Khaki Field Day Date and Pan-Europ Auto. Practically the same for owners.
• ETA 2836-2. The older 4 Hz day-date Swiss movement, with about 38 hours of reserve. Smoother sweep and easier independent servicing, but it won't make it through a weekend off the wrist.
• Seiko 4R35/4R36. The 4R36 day-date version is in many Seiko 5 Sports models. Cheaper to replace, about half the reserve and a looser factory tolerance.

Living with the 80-hour reserve

Take your Khaki Field King off at 6pm on Friday and, if it was fully wound, it's still running at 2am on Tuesday, with the day and date correct. That last part is the real benefit on a day-date watch: when a 38-hour movement stops over the weekend, you have to reset the time, the date and the day, which on some models means cycling through several days.

The catch is "fully wound". A Jazzmaster Day Date worn for a short evening won't have anything like 80 hours in it. Watch Winder counts down the reserve for each watch you own and reminds you before it stops, so you can top it up and skip the day-date reset. To check a particular weekend, try the "Will my watch stop?" calculator.

Verdict

The H-40 is what makes the Khaki King such a practical day-date watch: 80 hours of reserve means you rarely have to reset the calendar. It's reliable and usually accurate, and the newer versions add a Nivachron balance spring. The trade-offs are the usual ones for the family: a slightly slower sweep, no published accuracy spec, some variation between watches, and a service system that prefers swapping movements to overhauling them.

FAQ

How long does a Hamilton Khaki King run off the wrist?

About 80 hours when fully wound, a little over three days. Take it off on Friday evening and it should still be running on Monday morning.

What movement is in the Hamilton Khaki Field King?

The H-40, an automatic day-date movement from the Swatch Group's Powermatic 80 family, with 25 jewels, 21,600 vph and an 80-hour reserve. The 2026 Day-Date version adds a Nivachron balance spring.

Does the Hamilton Khaki King hack?

Yes. The H-40 stops the seconds hand when you pull the crown out to set the time, and it can be wound by hand.

How accurate is the Hamilton Jazzmaster Day Date?

Hamilton doesn't publish an official accuracy figure for the H-40. Many owners report single-digit seconds a day, and a watch running well outside that when new can be regulated under warranty.

What movement is in the Khaki Aviation Pilot Day Date?

Hamilton lists the current Khaki Aviation Pilot Day Date Auto, reference H64615135, with the H-40 and a Nivachron balance spring, but the H64635 references with large numerals use the closely related H-30. Check your specific reference.

Is the H-40 the same as the H-10?

They share the same C07 base, 3 Hz beat and 80-hour reserve. The H-40 adds a day wheel and day-date display; the H-10 is time-only or time and date.

Why is the day wrong on my Khaki King after it stopped?

When a day-date watch stops, the calendar stops too. Set the day and date with the hands well away from midnight, then set the time, making sure AM and PM are right.

Sources

• Hamilton: Khaki Field King Day-Date H64475531
• Hamilton: Khaki Aviation Pilot Day Date Auto H64615135
• aBlogtoWatch: Hamilton Khaki Field King review
• Worn & Wound: Hamilton 2014 preview
• Uhrenwerkstattforum: acceptable rates for a Hamilton H-40 (C07.641)

Watches we've reviewed with the Hamilton H-40

• Hamilton Khaki Field King review

Keeping it running

• On an average day an automatic gains roughly 4 hours of reserve per hour on the wrist, so about 20 hours of wear fills the Hamilton H-40. Desk days charge more slowly.
• Most automatics can also be wound by the crown. If yours has stopped, a few dozen turns gets it going before you put it on.
• Off the wrist it stops about 80 hours after it was last full. Stopped sooner?
• On a watch winder, start at about 650 turns per day, both directions. Winder settings for every movement.
• If it does stop, don't set the date between 9pm and 3am. Check if it's safe.

All Hamilton movements · Other 80-hour movements

Never let it stop

Watch Winder counts down the reserve of every watch you own and reminds you before one stops. It already knows the Hamilton H-40: type your watch's name and the reserve fills itself in.

Manufacturer's published figure. Real reserve varies with the watch's age and service; check your manual.