Hello Gaurav,

When a vessel shell is rolled from a plate into a cylinder, it might not be perfectly round. The 'e' value is the maximum diameter minus the minimum diameter divided by the average diameter - basically.

The graph in Figure UG-80.1 is only a representation of the value 'e'. UG-80(b)(2) discussed the value of 'e' when consideration is given to external pressure. A careful reading of that paragraph states what to do when values fall off the graph.