Bike chains are the same all around the world, made of links half an inch long. During its lifetime it will gradually stretch, depending on how much load you put it under, and if it stretches too much then it will start to wear out other drive-train components (the front chainrings and rear cassette) at a much faster rate. The accurate way of checking how much your chain has stretched is with a chain checker tool, and it will tell you the stretch amount (as a percentage).
I have opted for the Park Tools CC-2 Chain Checker. It has a couple of pins sticking out, one of which is movable using a little lever. Having lined up the chain checker correctly against the chain, you move the lever out until the movable pin is snug against the relevant chain link - and then just read off the % stretch reported by the tool. Anything at 0.5% stretch or less is fine; anything at 0.75% or above is not. (Note that this is a usual guide; your particular chain may have other instructions!)
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