When Huo Gang took it out, he immediately felt that its weight was almost the same as steel, but it was extremely hard, obviously made of alloy, I am afraid it was difficult to deform, and the accuracy on it was extremely fine, of course, the smallest accuracy was also millimeters.

And when Huo Gang focused his attention on this ruler, the Spirit of the Jade Gate gave a rare explanation, this material is made of a special nickel-iron alloy, it is in the room temperature range of plus or minus tens of degrees Celsius, and its thermal expansion coefficient is zero! In other words, it is at room temperature, and there is no thermal expansion and contraction.

This is one of the reasons why it is used as a standard weight and scale unit of length.

Taking out this ruler, Huo Gang handed it to Sun Er, and then said: "This is the weights and measures we will use in the future, this is a unit of length, this ruler I call it a meter, a ruler is one meter, these large scales above are decimeters, one meter is equal to 10 decimeters, the smaller ones are centimeters, the same decimeter is also equal to ten centimeters, the smallest is millimeters, one centimeter is equal to ten millimeters, and the decimal system is used." ”

Taking over the ruler in Huo Gang's hand, Sun Er and the others were stunned, because they were all craftsmen, so they could clearly know how strong the technology needed to be to process steel into this way!

Don't look at it as just a ruler, but this ruler can be seen in the eyes of these craftsmen, how technical it is! If it weren't for some great craftsmen, it would not have been possible to do it!

Especially the scales above, they are so fine, and they are extremely precise between each scale, and you can see at a glance that these scales are exactly the same between them.

And the shades of these scales look almost identical.

What's even more terrifying is that when you look at it from the side, you can see the scale on it, but when you look down from the vertical direction, you will think that it is just a flat iron ruler, without any scale, you can imagine how fine the scale is!

Of course, this is not the only one for measuring units of length, but also a mechanical type of vernier caliper made of the same material.

As soon as the vernier caliper was taken out, Lu Mu couldn't help but speak: "General, how is this caliper made?" This one is too delicate! This...... unimaginable. ”

Hearing Lu Mu's words, Huo Gang was slightly stunned, is there a caliper at this time? Huo Gang really doesn't know this, he is not omnipotent, how many things have been invented in ancient China, how can Huo Gang know.

However, since Lu Mu called out its name, although it is not an accurate vernier caliper, a caliper is enough to explain everything.

"Yes, I call it a vernier caliper, and it's primarily a precision measuring tool."

"This whole set of length units is mainly used as a master, let you use it as a material, and then imitate it, and then we will directly implement it on a large scale." Huo Gang said very simply.

"Yes." Lu Mu and the others looked at each other, and then immediately bowed down and spoke. Although this is different from the weights and measures they have learned, they also know that at this time they are few people, and it is easiest to start implementing weights and measures.

When there are more people in the back, it will be more difficult to popularize it on a large scale.

Now that there are few people, you can teach some people first, and it will be more convenient for people to pass on later.

The length of the ruler, as the real master is this ruler, and this vernier caliper. And like this, there are ten sets in total. But that doesn't mean that's all the tools, and there are also ten sets of rulers like tape measures, and there are three to ten meter tape measures.

In this era, this thing really can't be produced.

When they didn't see Lu Mu pull out the tape measure, people were stupid, they couldn't imagine how this made steel so light and thin, and more importantly, so light and thin, but so difficult to deform.

At least they simply can't do it.

In addition to the unit of length, it is the unit of weight, and the unit of weight is simple. The same is a complete set of weights made of special alloys, from the smallest one gram, two grams, five grams, ten grams, and then to one kilogram of weights, the same set of ten.

Not only that, but there are also ten scales here.

Then there are the weights and measures of volume, but there are not many weights and measures of volume, only liters and milliliters. Because liters can be converted to cubic meters.

In addition to this, there is the thermometer, which is the most common mercury thermometer, and the material is made of special materials, which can test the temperature of up to 300 degrees Celsius, because beyond this temperature it is close to the boiling point of mercury.

Other than that, there is nothing else.

Huo Gang thought that he could give a clock or something, but it seems that if he wants to give Huo Gang a clock, then at least there must be an atomic clock, because other clocks are not accurate.

But atomic clocks are clearly too high-end in this day and age.

But while there are only four types of weights and measures, they are actually sufficient.

Because the longest used weights and measures in this era are these four things, as for the other weights and measures, if you really calculate them, it is really too high-end. That's where basic science needs to be popularized.

At least there is no unit of time at the moment, and I don't know if there will be one in the future.

But even so, when these units of measurement were handed over to Sun Er and them, they were extremely serious, and in their opinion, this meant that they were more important than their ancestors.

"General, what does this symbol mean on this?" Lu Mu asked curiously, pointing to the Arabic numerals on the ruler.

Huo Gang looked at it, and he was a little helpless, could it be that he had to act as a teacher once in this world?

"These are Arabic numerals, a form of counting in arithmetic...... It was invented by a scientist on the big food side, and it worked so well that I introduced it. Huo Gang roughly explained that although it is called Arabic numerals, the person who invented it seems to be an ancient Indian, but it was carried forward by the Arabs, so it is called Arabic numerals.

Huo Gang was very curious when he saw them, so Huo Gang thought about it, and simply handed over these numbers to them, just teaching them to recognize these numbers is actually very simple, these craftsmen are not stupid, so it is a quarter of an hour, and almost all the craftsmen remember it.

"This ...... This number is very useful. It's more intuitive than the numbers we use, and it's less error-prone when it comes to recording. Although Rumu was not an arithmetician, the carpenter had the most contact with arithmetic, so he immediately felt the superiority of Arabic numerals compared to traditional numbers.

"Yes, I'll give these things to some gentlemen, and they'll write them into a book, and we're going to promote them in the future." Huo Gang thought about it and immediately spoke. Because of the popularization of Arabic numerals, it is a big advantage for bookkeeping, and ordinary people want to understand the ancient ledger, but it is not so easy.

But Arabic numerals are much more intuitive.