This means 18 change of phase movements of the packets. Closer examination reveals that other modes could be thought of in the same manner. The first TFS mode has one phase change among the blades in the packet so it can only have a minimum of 9 ND which means the TFS1 mode picks up where the first tangential mode leaves off. The fifth TFS mode with five phase changes within a packet can have the maximum number of nodal diameters, 54. That is, all the blades within the wheel are moving out of phase with one another.
Solid circles represent single modes and the unfilled circles represent double modes.
A nodal diameter will occur 90 from the first. Except for 0 and 54 ND, the other single modes are really separated double modes. For example, the 9th ND could describe either the first tangential or the 1st TFS mode. Completing construction of the SAFE diagram requires plotting of the excitation phenomena. On the Campbell diagram, possible excitations are presented by diagonal lines.