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If you've set up another Apple Watch with your current iPhone, a screen appears that says Make This Your New Apple Watch. Tap Apps & Data and Settings to see how Express Setup will configure your new watch. Then tap Continue. If you want to choose how your new watch is set up, tap Customize Settings. Then choose a backup from another previous Apple Watch to restore. Or tap Set Up as New Apple Watch if you want to fully customize your new device's settings.

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Your Apple Watch might also require a software update on your iPhone before you can set up the watch. If your iPhone says that a software update is available, tap Update Now and wait for the update process to finish.

Your Apple Watch shows the watch face when the pairing procedure is finished and your watch is ready to use. Keep your Apple Watch and iPhone close together so the devices can continue syncing information in the background.

In the world of modern portable devices, it may be hard to believe that merely a few decades ago the most convenient way to keep track of time was a mechanical watch. Unlike their quartz and smart siblings, mechanical watches can run without using any batteries or other electronic components.

In a functioning watch many parts are in constant motion. By default all animations in this article are enabled, but if you find them distracting, or if you want to save power, you can globally pause all the following demonstrations.disabled, but if you prefer to have things moving as you read you can globally unpause them and have animations running.

These gears are intended to work with each other so the ratio of teeth is equivalent to the ratio of the gear radii. When the driving gear has more teeth than the driven gear, the driven gear makes more rotations than the driving gear. We can use this behavior to make the second hand of a watch rotate many times on a single rotation of the barrel.

Before we finish up with gears, let me quickly mention the shape of their teeth. While many bigger machines use an involute shape for the profile of their gear teeth, mechanical watches commonly use cycloidal profiles which are obtained by rolling a circle on the surface of another circle.

By carefully tuning these parameters, we can make this system oscillate at a desired rate. This idea of using a torsion spring with attached mass is exactly what mechanical watches use as their source of precise time tracking. The balance is formed by the balance wheel attached to the balance spring. In this watch the balance wheel oscillates back and forth at a fairly high frequency:

In this watch movement the balance wheel does a full back and forth swing four times per second, hitting the pallet fork twice during each cycle, for a total of 8 beats per second or 28,800 beats per hour. While different watches may have different rates, they all do a tiny turn of the second hand many times per second, which gives mechanical watches the illusion of a very smooth hand motion.

Notice that a jewel has a small basin in it. To even further reduce energy losses of the rotating components, a small amount of special oil is placed in that cavity. That oil sticks to the jewel and a shaft that rotates inside it to further decrease the friction, which lets the watch run longer on a single wind, while also reducing wear on the delicate mechanical parts.

When the watch is shaken, the motion of the shaft is absorbed by the spring, similarly to the suspension system in a car. If the jerk is very strong, then the much thicker and stronger part of balance shaft carries the load through the case, which protects the fragile tip from breaking.

In our movement, the second hand is cleverly mounted on the fourth wheel of the power train since that wheel rotates once per minute with high precision. For the minute hand to turn at the correct pace, we need some axis to rotate 60 times slower than that. Thankfully, the designers of this watch movement used an ingenious way to harness some of that speed reduction from the other gears.

If you look closely, you can see that the small gear of the third wheel from the other side of the watch is exposed through a little opening. We can mount a cannon pinion with its driving wheel onto the center of the watch and have that driving wheel mesh with the small gear:

With every step our watch is becoming more complete, but we still have a few inconveniences in our way. To change the time and to wind the mainspring, we have to turn the internal gears of the movement, which normally are safely hidden inside the watch case.

When the person wearing a watch moves arms throughout the day, the orientation of that watch in space changes quite a lot. Even during a leisurely walk, the watch swings slightly relative to the ground. Normally, all the energy used to move the watch goes to waste, but an automatic winding mechanism manages to capture some of it to wind the mainspring.

If you recall our discussion of watch winding, you may remember that the ratchet wheel can only turn in one direction with the click preventing the mainspring from just unwinding on its own. However, the weight can swing back and forth, which would normally imply that any gear system that is connected to that weight would also rotate in both directions.

There are many YouTube channels dedicated to mechanical watches, but I particularly like Wristwatch Revival, which is dedicated to fixing broken watches, which very often involves a complete dissection of a movement, and a repair or replacement of broken parts. Although the creator is not a professional watchmaker, the videos are packed with information and are very enjoyable to watch.

In the 1970s mechanical watches started to be dethroned by quartz models, which track time by electronically counting vibrations of a quartz crystal. As technology progressed, typical watches only increased their reliance on digital circuits. Modern smart reincarnations resemble their archetypes only in shape and placement on wrists.

Mechanical watches are not as accurate as digital ones. They require maintenance and are more fragile. Despite all these drawbacks, these devices show a true mastery of engineering. With creative use of miniature gears, levers, and springs, a mechanical watch rises from its dormant components to become truly alive.

watch is shallow by default: the callback will only trigger when the watched property has been assigned a new value - it won't trigger on nested property changes. If you want the callback to fire on all nested mutations, you need to use a deep watcher:

Deep watch requires traversing all nested properties in the watched object, and can be expensive when used on large data structures. Use it only when necessary and beware of the performance implications.

watch is lazy by default: the callback won't be called until the watched source has changed. But in some cases we may want the same callback logic to be run eagerly - for example, we may want to fetch some initial data, and then re-fetch the data whenever relevant state changes.

It is common for the watcher callback to use exactly the same reactive state as the source. For example, consider the following code, which uses a watcher to load a remote resource whenever the todoId ref changes:

Here, the callback will run immediately, there's no need to specify immediate: true. During its execution, it will automatically track todoId.value as a dependency (similar to computed properties). Whenever todoId.value changes, the callback will be run again. With watchEffect(), we no longer need to pass todoId explicitly as the source value.

For examples like these, with only one dependency, the benefit of watchEffect() is relatively small. But for watchers that have multiple dependencies, using watchEffect() removes the burden of having to maintain the list of dependencies manually. In addition, if you need to watch several properties in a nested data structure, watchEffect() may prove more efficient than a deep watcher, as it will only track the properties that are used in the callback, rather than recursively tracking all of them.

watch only tracks the explicitly watched source. It won't track anything accessed inside the callback. In addition, the callback only triggers when the source has actually changed. watch separates dependency tracking from the side effect, giving us more precise control over when the callback should fire.

watchEffect, on the other hand, combines dependency tracking and side effect into one phase. It automatically tracks every reactive property accessed during its synchronous execution. This is more convenient and typically results in terser code, but makes its reactive dependencies less explicit.

By default, user-created watcher callbacks are called before Vue component updates. This means if you attempt to access the DOM inside a watcher callback, the DOM will be in the state before Vue has applied any updates.

Watchers declared using the watch option or the $watch() instance method are automatically stopped when the owner component is unmounted, so in most cases you don't need to worry about stopping the watcher yourself.

Watchers declared synchronously inside setup() or are bound to the owner component instance, and will be automatically stopped when the owner component is unmounted. In most cases, you don't need to worry about stopping the watcher yourself.

The key here is that the watcher must be created synchronously: if the watcher is created in an async callback, it won't be bound to the owner component and must be stopped manually to avoid memory leaks. Here's an example: 041b061a72