When you want to figure out if someone would be a good fit for a senior position at your company, you 'ask around.' You find multiple people who know the person then you ask them all the same questions about the person you maybe want to hire. Ordinarily speaking, they will all give similar answers, so asking them all may at first seem redundant; but the reason you used multiple references is to be sure that you are getting an accurate impression. You amalgamate their answers to arrive at a more accurate one.

 

This is similar to the way in which GPS systems work. Every device that tells you your location based on GPS is constantly 'listening' for signals from GPS satellites, of which there are thirty (positioned so, at any given time, you have a direct line with at least four). Once it 'hears' a signal from a GPS satellite, it calculates how far away it is based on the delay in its response. Then, your device calculates your location by comparing the delays from multiple satellites.

 

The Global Positioning System was created by the US Air Force and was originally designed for military use only. It consists of both satellites (to produce the measuring signals) and ground-based stations (to pinpoint where the satellites are). GPS satellites are equipped with atomic clocks to help them accurately measure time, but they must adjust their timekeeping for relativity as they are a) in low gravity and b) moving quickly.