Use two sliders to change a plot - not using GUIDE

I would like to change my grap of sin(x*a)+m controlling a and b by using two sliders. This is my code, how could I modify commented code to make it work?

function plot()
close all

    %# setup GUI
    hFig = figure('menu','none');
    hAx = axes('Parent',hFig);

    %first slider
    uicontrol('Parent',hFig, 'Style','slider', 'Value',1, 'Min',-1,...
        'Max',4, 'SliderStep',[0.05 0.1], ...
        'Position',[150 5 300 20], 'Callback',@slider1_callback) 
    hTxt1 = uicontrol('Style','text', 'Position',[460 8 20 15], 'String','0');

   %     %second slider
   %     uicontrol('Parent',hFig, 'Style','slider', 'Value',1, 'Min',-1,...
   %         'Max',4, 'SliderStep',[0.05 0.1], ...
   %         'Position',[150 35 300 20], 'Callback',@slider2_callback) 
   %     hTxt2 = uicontrol('Style','text', 'Position',[460 38 20 15], 'String','0');

    %# Callback function
    function slider1_callback(hObj, eventdata)

        a = get(hObj,'Value');
        m = 1;                 %***I wish it depends by the second slider***
        x = -3:0.001:3;
        y=sin(x*a) + m;
        plot(hAx,x,y,'.r')

        set(hTxt1, 'String',num2str(a))       %# update text
   %         set(hTxt2, 'String',num2str(b))       %# update text

       % # Callback function
   %     function slider2_callback(hObj, eventdata)

   %         a = 1;                 %***I wish it depends by the first slider***
   %         m = get(hObj,'Value');
   %         x = -3:0.001:3;
   %         y=sin(x*a) + m;
   %         plot(hAx,x,y,'.r')
   %         set(hTxt1, 'String',num2str(a))       %# update text
   %         set(hTxt2, 'String',num2str(b))       %# update text
   %     end

    end
   end