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A unit vector is labeled d s sub z equals z caret r d r d phi. Another unit vector is labeled d s sub r equals r caret r d phi d z. The differential volume is labeled equals d V equals r d r d phi d z. The vector in phi z cylindrical surface is d s sub r equals r caret d l sub phi d l sub z equals r caret r d phi d z. The vector in r z plane is d s sub phi equals phi caret d l sub r d l sub z equals phi caret d r d z. The vector in r phi plane is d s sub z equals z caret d l sub r d l sub phi equals z caret r d r d phi.