How to set the XTick value based on a user defined variable in a GUI?

Hi all,

I am currently trying to make my axis tick distances vary based on the type of image that is being inserted into a GUI. I have two radio buttons that define a variable value. The variable should then correlate to the distance for each of the tick marks through a function. The code is shown below.

    function bitvalue_Callback(source,eventdata)
    source
        type1 = strcmp(source.String, '64bit');
        type2 = strcmp(source.String, '128bit');
        if strcmp(source.String, '64bit')
            set(S.rbDF_64bit,'Value',1);
            set(S.rbDF_128bit,'Value',0);
            bitvalue = 64;
        else
            set(S.rbDF_64bit,'Value',0);
            set(S.rbDF_128bit,'Value',1);
            bitvalue = 128; 
        end

    end

    function pbDF1_Mon_Callback(source,eventdata)
        source
        get (bitvalue);
        [ImFile,folder] = uigetfile('H:\New_CHAR_GUI\New Version 04\Sample Data\*.*');
        Im = imread(fullfile(folder,ImFile));
        ImPos = strcmp(source.String,'Insert 1');
        if ImPos == 1
        Im_axes = axes('Parent',S.tab(tab_num),'Units',...
              'normalized','Position',[0.015 .02 .98 1]);
        S.hDFplot = axes('Parent',S.tab(tab_num),'Position',[0.015 0.375 0.98 .287], 'color','none','XAxisLocation','top',...
            'Xlim',([0,102]),'XTick',linspace(0,102,(bitvalue./52)),'fontsize',7,'Ylim',([0,700]),'YDir','reverse','YColor','none');
        xlabel('Delay / {\mu}s','FontSize',8)
        box on
        grid on
        grid minor
        tex_ax_Pos = [S.hFPWplot_Pos(1) 0.05 S.hFPWplot_Pos(3) 0.1];
        tex_ax = axes('Parent',S.tab(tab_num),'Units','normalized','Position',tex_ax_Pos);
        set(tex_ax,'Visible','off','Color',[242/255 242/255 242/255])

        else
            Im_axes = axes('Parent',S.tab(tab_num),'Units',...
                'normalized','Position',[0.015 -.327 .98 1]);
        S.hDFplot = axes('Parent',S.tab(tab_num),'Position',[0.015 0.030 0.98 .287],...
            'color','none','XAxisLocation','top',...
            'Xlim',([0,102]),'XTick',linspace(0,102,(bitvalue./52)),'fontsize',7,'Ylim',([0,700]),'YColor','none');
        xlabel('Delay / {\mu}s','FontSize',8)
        box on
        grid on
        grid minor
        tex_ax_Pos = [S.hFPWplot_Pos(1) 0.05 S.hFPWplot_Pos(3) 0.1];
        tex_ax = axes('Parent',S.tab(tab_num),'Units','normalized','Position',tex_ax_Pos);
        set(tex_ax,'Visible','off','Color',[242/255 242/255 242/255])

        end