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@531
Chainline for a single sprocket (fixed) is pretty simple. The same principles apply to double/triple chainwheels, and multiple sprockets. First measure the diameter of the seat tube close to the chainring (say 30mm) and divide by 2 =15mm. Then measure from the seat tube to the teeth on the chainring (say 27.5mm) for triples this should be to the centre ring, and for doubles to between the rings. The chainline would then be 27.5 + 15mm = 42.5mm.
For the back wheel measure the width between the fork ends. Usually 120mm single speed, around 126mm for 5 to 7 speed, and multiple gears 130-135mm. Divide this by 2, say 60mm. Last measurement use a flat (check it on plate glass) 10mm open ended spanner, and bolt it on to the axle on the sprocket side of the wheel. Measure from the inner flat to the sprocket teeth say 17.5mm. For multiple sprockets measure to the middle cog teeth. The chainline for the wheel is therefore 60mm minus 17.5mm = 42.5mm. Differences can usually be adjusted by using chainring spacing washers, or spacers on the rear wheel.