Sailors in the past had a similar adage: “Never go to sea with two chronometers; take one or three.” They relied on precise clocks to calculate longitude.

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maxbond an hour ago | parent | next [-]

I think it is different in the continuous case though, because you can average two (reasonably accurate) chronometers and get a better measurement. But we can't average true and false, at least not in the context of this problem definition.

But the chronometers are will sync with each other if you don't store them apart, which would result correlated noise that an average won't fix.

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jethro_tell 23 minutes ago | parent [-]

You can definitely average two relatively accurate chronometers but you if you only have two it’s difficult to tell if one is way fast or way slow.

In a perfect world they drift less than a minute per day and you’re relatively close to the time with an average or just by picking one and knowing that you don’t have massive time skew.

I believe this saying was first made about compasses which also had mechanical failures. Having three lets you know which one failed. The same goes for mechanical watches, which can fail in inconsistent ways, slow one day and fast the next is problematic the same goes for a compass that is wildly off, how do you know which one of the two is off?

	▲	maxbond a minute ago \| parent [-]
		> In a perfect world they drift less than a minute per day... A minute per day would be far too much drift for navigation, wouldn't it? From Wikipedia [1]: > For every four seconds that the time source is in error, the east–west position may be off by up to just over one nautical mile as the angular speed of Earth is latitude dependent. That makes me think a minute might be your budget for an entire voyage? But I don't know much about navigation. > Having three lets you know which one failed. I guess I hadn't considered when it stops for a minute and then continues ticking steadily, and you would want to discard the measurement from the faulty watch. But if I just bring one watch as the expression councils, isn't that even worse? I don't even know it malfunctioned and if it failed entirely I don't have any reference for the time at the port. My interpretation had been that you look back and forth between the watches unable to make a decision, which doesn't matter if you always split the difference, but I see your point. [1] https://en.wikipedia.org/wiki/Marine_chronometer

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patja an hour ago | parent | prev [-]

I am a sailor in the present and this same rule is why I have 3 digital multimeters on my boat.

	▲	jethro_tell 22 minutes ago \| parent [-]
		Two is one and one is none