NCSL International is an organization that helps people who work in science, technology, engineering, and math (STEM) make sure their measurements are accurate.
Basically, when scientists and engineers make things, they need to measure things like temperature, weight, and length really precisely. If they don't measure things accurately, they might make a mistake that could hurt people or waste a lot of time and money.
NCSL International helps scientists and engineers learn about new technologies and techniques for measuring things accurately, and they make sure that everyone is using the same standards for measuring things. That way, when people share their research with each other or with the public, everyone can trust that the measurements are accurate and true.
It's like if you and your friends were all drawing pictures of your favorite animal, and you all agreed that you would use the same size paper and the same color pencils. That way, when you show your pictures to your other friends, everyone knows that they're looking at the same thing!