Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

The League of SI Superheroes is Running Out of Time!

The League of SI Superheroes is back!

Working from their not-terribly-secret HQ at the National Institute of Standards and Technology (NIST), the cartoon heroes of the metric system use their awesome powers of measurement to fight uncertainty, imprecision and inaccuracy and to improve our daily lives.

In their newest adventure, Running Out of Time!, the League encounters an old foe, Major Uncertainty, who is meddling with the atomic clocks that are responsible for the accuracy of the Global Positioning System.

Will the League foil the evil alien? Will the GPS system be fixed in time? Will a lost father and son find their way to the Grand Canyon?

Watch and find out!

Running Out of Time!
Running Out of Time!

The new League adventure highlights the importance of precision time-keeping to the widely used Global Positioning System. The GPS uses a constellation of at least 24 satellites. Highly accurate atomic clocks on the satellites enable them to provide precise geographic position data to people with a GPS receiver—generally to within a few meters.

First introduced in Desperate Measures (2014), the League of SI Superheroes encourages students to learn about metric measurements as they consider science, technology, engineering and mathematics (STEM) careers. SI familiarity and fluency must be developed along the STEM career pipeline to prepare future workers with essential measurement skills.

Modeled on the seven base units of the International System of Units, or SI, the League of SI Superheroes are:

  • Meter Man: With his laser interferometer eyes, graduated arms and extendable body, no dimension is too big or too small for Meter Man to measure.
  • The Mole: Able to sniff out and count the atoms of every element, the Mole is a master of chemistry.
  • Professor Second: By reading the vibrations of her laser-cooled cesium atoms, Professor Second can synchronize any frequency and calibrate any clock.
  • Monsieur Kilogram: Monsieur Kilogram loves lifting weights, and it shows. With his balance scale arms, no mass is too big or too small for him measure.
  • Ms. Ampere: Ms. Ampere rules the flow of electrons—electrical current—and makes sure that the right amount gets where it needs to go.
  • Dr. Kelvin: Dr. Kelvin heats up or cools down objects by speeding up or slowing down the particles inside them. He can also measure the temperature of anything in the universe with his trusty thermometer.
  • Candela: Don't let her small size fool you. Candela's power over light helps to brighten the whole world.

Catch up on their adventures at Teachers can also request a classroom set of SI educational materials by submitting their contact information and grade level to TheSI [at] (TheSI[at]nist[dot]gov).

Released May 29, 2015, Updated January 25, 2023