Question

What is sigma uncertainty?

Answer 1

Answer:

1 sigma = 68 %, 2 sigma = 95.4%, 3 sigma = 99.7 %, 4 sigma = 99.99 % and up. Another way to think of this is by taking 1-Probability. So, 1 sigma means that 32% of the time, you don't measure 45 +/- 10 km/s. At 3 sigma, you don't measure 45 +/- 10 km/s only 0.3% of the time.