This "trick" is a "practical" way to estimate the time left before sunset. The approximate amount of daylight remaining until the sun sets. Count the number of hands above the horizon...
For example, estimating the time needed to find (or make) shelter during an outdoor excursion. Or the time remaining to move without the aid of a flashlight or headlamp. Estimate the time remaining to complete necessary tasks before sunset (gather wood, light a fire, prepare dinner, etc.)
This method works for an average adult with an outstretched hand.
Each finger corresponds to approximately fifteen minutes of remaining daylight . Four fingers therefore correspond to approximately one hour.
Here's how to do it:
1. Stretch your arm out in front of you toward the sun. Bend your wrist so that your palm is facing you and your hand is horizontal with your thumb on top. The bottom of the sun should rest on the top of your index finger.
2. Place the other outstretched hand under the first.
3. Now place your top hand under the second and continue to "walk" with your hands towards the horizon, counting the hands as you go. 
Keep your arms straight as you slowly lower both hands toward the horizon.
Don't neglect this method by using only one hand or placing your hand too close to your face because your elbows are bent. The arms are straight. I'm just saying it.