This option allows the user to change the relative positions of a set of neighbouring gel readings starting at some fixed gel reading. Hence it can be used to change the alignment of gels within a contig. It prompts for the number of the first gel reading to shift and then then relative distance to move by. A negative shift will move the gel leftwards.
Then this gel and all its rightward neighbours are moved by this amount. Tags on the gels and consensus are moved accordingly. It also automatically updates then length of the contig.