no proven facts?

I think of facts as an agreement truth as our personal subjective truth

I am not sure what you call your measurement for length: inches and feet and miles etc... The British call it imperial. I live in a British colony, aka Australia. In GB, aka UK, there exists a strong belief that the sky, or skies, would cave in if the poms intruduced the metric system. Those used to using the system will tell everyone who is not that the system is better. For them that is a fact. Fact are convenient to stop discussions.
As a matter of "fact" what people really mean is the a decimal system is better and by better they mean more convenient to used. You, and here I assume that the majority in this group are imperialists, so you the imperialists might argue about the qualitative advantages. On the other hand you will accept the existence of the metre as fact.
But does the metre exists? As someone mentioned facts are the result of consent.
All ISO norms are the result of conventions between different groups.
How can someone prove the existence of the measurement known as metre?
Go to the office and check it out. Today 1 metre should just be the same length it was when it was "invented". The interesting fact is the definition of a a metre has changed over time, but its length hasn't.

@gater Convincing evidence, yes. Fact by consensus, yes. But proof in any absolute or scientific sense? How would you do it?
Analytical logical proof does not apply and the scientific method requires something that strictly reproducible.

@PontifexMarximus Actually, even the official length of a metre, or meter, has changed over time.
The metre was originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole. In 1799, it was redefined in terms of a prototype metre bar (the actual bar used was changed in 1889). In 1960, the metre was redefined in terms of a certain number of wavelengths of a certain emission line of krypton-86. In 1983, the current definition of the length of the path traveled by light in a vacuum in 1/299,792,458 of a second.

@Heraclitus correct ... The idea of measuring the circumference of the earth was interesting ... Apparently one guy measuring the distance from Dunkerk to Barcelona cheated ... And the was a discrepancy of 3 mm ... As to the latest definition ... Who would have the technical means to verify that fact?

@Bobby9 That's not history.

@Bobby9 I can't really tell if you are just joking or not. I suspect that you are. But if you really don't know the difference between historiography and basic scientific facts, then I have no idea what to say to you.

@Bobby9 LOL!

@Bobby9 Now you are just being plain silly. Do you have the slightest idea what historiography is? Do you really think that I, or anyone on this website, is disputing that 1+1=2?

can you prove 2+2 is always 4?

@gater take 2 and 2 of anything anytime. You'll see that when you combine them, you'll always have 4 of those things.

@TheMiddleWay didn't know what that was called, but thanks for the insight?

@Bobby9 TheMiddleWay is making valid points. Let's see if I can put it into different words.

One of the points he's making with his "apples and oranges" example is that depending on how you're system of categorization operates, you can only have 2 and 2 and not 4. If you're adding "things" to "things", then you'll have 4 "things" when you combine the apples and oranges. But, if you're going to be more specific in your categorization, and you differentiate between apples and oranges, then when you combine the 2, you'll only have 2 and 2 and not 4.

The mechanics of addition vary when you consider the nature of the things you deal with and what you are trying to accomplish by adding.