Rotor alignments basically refer to aligning coupling rim and face to maintain concentricity and parallelism. Ideally, a perfectly aligned coupling has zero eccentricity at the coupling joints. This results in zero unbalance excitation at the couplings, and hence a good shaft system alignment can be maintained. In reality, some amount of eccentricity always exists that could trigger low levels of vibration and could add to overall shaft vibration. The coupling alignment data is discussed in detail in the next section using laboratory couplings