Garage Door Springs

I have two garage doors. The torsion spring on one broke several months ago so I took the spring off of the side that isn't used but about 4 times a year and replaced the broken one. Now it is time to put a spring on the side that doesn't have one.



I have measured the length of the spring I have but in looking at other springs I have noticed that they are left or right hand wound. How do you tell the difference and what difference does it make how they are wound?



thanks



Syb