Understanding color ratios

HTML-CSS
1

In the lesson:

https://www.freecodecamp.org/learn/responsive-web-design-v9/lecture-user-interface-design-fundamentals/how-do-you-create-good-background-and-foreground-contrast-in-your-designs

it talks about color contrast and uses ratios to demonstrate whether different colors have good contrast to each other or not. I understand this is a difference in luminance between colors. However some some color ratios have a third number ie. “10:34 :1”. The third number appears to always be a one. What does the third number stand for?

2

It’s not 10:34:1 but rather 10.34:1. (A ratio of 10.34 over 1. There’s a decimal, not a colon, between 10 and 34.)