Hatch,
this is concerned with the roll shape deflections occuring due to roll chatter.To elucidate further, the text matter reads as follows:
The fig.(referring to modal deformation of mill with strip) seems to correspond to fifth-octave-mode of chatter on sheet mills.
After going through this text material* i got the above question.
*Flat processing of steels ------- William Roberts (pg. 597)