GUI for manipulating data in a figure

GUI to move a selected data point upward or downward by a user-defined amount
% Input: nfig -- the number of the figure
% Use: 1. push the "Select" button
% 2. move the mouse unto th figure to select a data point to be
% moved
% 3. push "Up" or "Down" button to move the data point
% 4. push "Undo" button to cancel the previous move
% 5. change the delty if needed
%
% Note: This function is not to be used against the rule "data is data"; rather, it is to help one
% to plot data correctly, e.g. when plotting phase vs frequency in
% spectrum analysis, one may need to move some phase data by 360,
% 2*pi, or 1 depending on the unit of the phase is degree, radian or
% period.
%
% These codes are also a good example of GUI development