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Independently Adjustable Hour Hand (IAHH)
A watch with independently adjustable hour hand or 'IAHH' refers to the ability to move the indicated time on a watch forwards or backwards by whole hours1 without disturbing timekeeping. Every 'traveler' GMT watch has an IAHH, but there are 3-hand watches with IAHH as well.
Submitting my new article on this topic with:
a) the 3 reasons for IAHH
b) comparison of pusher vs. crown adjustment
c) electronic and mechanical implementations
d) 2 recent patents in IAHH adjustment feel
e) the complications of combining IAHH with simple, annual, and perpetual calendars
f) aside on the GMT hand stack
Here is the linl, no paywall: https://chmandaue.substack.com/p/the-independently-adjustable-hour
It can also be found on some very cheap movements but this isn’t well documented.
For example I bought a $50 brass case Timex chrono with an IHH a few years back.