Hagoromo's Fulltouch chalk has developed a cult following among mathematicians.
Some call it the Bentley of chalk, the Stradivarius of writing utensils.
Some say it's unbreakable.
Others say it leaves no dust behind.
The chalk has been called the math world's best kept secret.
The formula is still a secret and when the company announced it would cease production there was a mad rush to stock piles boxes of the chalk.
The Japanese chalk company was eventually saved by a South Korean investor.