Why are there two types of 'feet' in the United States that continue to use the imperial system hard?

As for the unit of length and weight, the internationally unified metric system is adopted in many countries. However, the imperial system is still used in the United States, which is the largest industrial country in the world. There are two types of length units 'feet' used in the imperial system, and it is expected that they will finally be unified in 2023.

America Has Two Feet. It's About to Lose One of Them. --The New York Times
https://www.nytimes.com/2020/08/18/science/foot-surveying-metrology-dennis.html

One of the unit that represents the length in the imperial 'feet' was originally in the unit system, which was based on the 'length of up to heel from the toe of the foot,' as its name, old is older than 4000 years Sumerian people It is said that he also used it.

There are mainly two types of such feet, 'surveying feet' and 'international feet'. Surveying feet is a unit established in the United States in 1893, and is '1 foot = 1200 meters in 3937 = 0.3048006096 ... meters'. On the other hand, international feet are defined as '1 foot = 0.3048 meters'. The reason why there are two feet is related to the long history of the system of units in the United States.

Immediately after independence, the United States decided to adopt the British imperial system as a unit system in 1790, and in 1815 standardized the American system based on brass standards made by London musical instrument craftsmen.

Then, in 1866, the US Parliament legalized the use of the metric system advocated in France, and in 1893 officially adopted the metric system as the American system of units. However, at this time, for some reason, it was decided that 'the length of 1 meter should be 39.37 inches' based on the old imperial system, so 12 inches = 1 foot became 0.3048006096 ... meters, which is a halfway number. The transition from the imperial system to the metric system was not well done. The surveying feet were set at this time.

In the 20th century, when mass production by machines began, processing with precision in units of comma millimeters was required. In addition, the different foot lengths used in the United Kingdom and Canada created the need for unification. Therefore, in 1958, six countries, the United States, the United Kingdom, Canada, Australia, New Zealand, and South Africa, signed an agreement, and it was accurately set as '1 foot = 0.3048 meters'. International feet are defined in this six-country agreement.

After that, basically all feet were unified to international feet in the United States, but only surveyors who surveyed the land continued to use survey feet. Land surveys and calculations require reference to old documents and data, all of which are recorded based on survey feet. If we were to unify with international feet, we would have to convert the huge amount of data contained in past materials, which would not be a business, so we were allowed to use survey feet.

At the time of writing, surveyors are required to use survey feet in most states in the United States, and some states do not specify which one to use. Since the regulations change from state to state, not from country to state, you may not notice that two types of feet are mixed when you move between states and survey. Only the United States uses two types of feet, so when an overseas surveying company participates in a project, they may not know that there are two feet, or the surveying software may only use international feet. There seems to be.

The difference between surveyed feet and international feet is only about 0.001 mm, so both seem to be almost the same, but they cause an error when dealing with vast lands. According to Arizona surveyor Michael Dennis, a two-foot error in the past caused a design error that blocked an international airport approach with a skyscraper under construction. It seems that he had hurriedly redesigned the skyscraper one floor lower.

'I've run into two different foot problems over and over, and I think it's ridiculous that this problem continues for years. I've wanted to abolish surveying feet for years. '.

Dennis, who wanted to abolish surveying feet, insisted that his boss, the director of the US National Geodetic Survey, 'should abolish surveying feet.' Furthermore, in April 2019, at a conference hosted by the American Surveyors Association, he strongly appealed that 'surveying feet are a victim of modernization.'

Then, the director of the American Surveyors Association agreed with the proposal to unify the international feet. 'We are not involved in the unification of feet, but we wanted to know the reaction of members of the American Surveyors Association,' the board commented. A subsequent survey found that most surveyors supported the unification of international feet. In addition, there was a voice from a small part that 'the abolition of surveying feet is a work close to blasphemy to God.'

Timothy Birch, chairman of the American Association of Surveyors, said, 'Surveying feet is the official name of the US survey foot, and unfortunately the abolition of surveying feet is'related to the United States for many Americans. It seems like things are being robbed and attacked. ”There are a certain number of people who are reluctant to abolish the units enacted in the United States, so the unification of feet has been debated so far. It is said that it was not. However, Birch says there is no reason to bother to leave surveying feet, as GPS-based accurate surveying is now possible without relying on ancient data.

Then, the National Institute of Standards and Technology, which defines the US unit system, decided to abolish surveying feet in October 2019, and declared that it would be unified to international feet on January 1, 2023. 'Unifying feet in the United States is a small step on the long road to standardization and accuracy. How conservative Americans are about the abolition of surveying feet is very conservative. There's something interesting about it. Thanks to science and technology, we haven't come up with the fact that we've learned a lot about the planet. '