How can I keep the proportion between the data and the values of axis?

Hello everyone. I am making a virtual oscilloscope in app designer, and I have troubles with plotting the right values. When in the default state, plotting shows the correct values of voltage on the X and Y-scale, but, when I turn the knob of the scope, the voltage is doubled when I decrease the vertical scale (a step on the Y-scale), otherwise the voltage is halved. I have attached the probe on the test voltage, which is squared, 5 volts. Does anyone know what could be the problem? I used the formulas for XData and YData from the code of scope's manufacturer. The same formulas were used for the other scopes. The images of my GUI are provided here: http://imgur.com/a/veKnf

if true
  % code
% Value changed function: AcquireDataButton
      function AcquireDataButtonValueChanged(app, event)
         app.AcquireDataButton.Value = event.Value;
          value = app.AcquireDataButton.Value;

            instrreset;
            visaAddress = 'USB::0x0699::0x03C6::C010224::INSTR';
            myScope = visa('tek', visaAddress);
            myScope.InputBufferSize = 4096;
            fopen(myScope);

            % Reset the oscilloscope to a known state
            fprintf(myScope, '*RST');
            fprintf(myScope, '*CLS');

            % Turn headers off, this makes parsing easier
            fprintf(myScope, 'HEADER OFF');

            % Autoset the oscilloscope 
            fprintf(myScope, 'AUTOS EXECute');

            %%Get record length value
            recordLength = query(myScope, 'HOR:RECO?');

            % Ensure that the start and stop values for CURVE query match the full
            % record length
            fprintf(myScope, ['DATA:START 1;DATA:STOP ' recordLength]);

            % Horizontal interval
            xIncr = query(myScope,'WFMOutpre:XINcr?');
            xIncr = str2double(xIncr);

            % Vertical offset
            fprintf(myScope,'WFMOutpre:YZEro?');
            vertOffset = fscanf(myScope);
            vertOffset = str2double(vertOffset);

            % Read YOFFSET to calculate the vertical values
            yOffset = query(myScope, 'WFMO:YOFF?');
            yOffset = str2double(yOffset);

            % Read YMULT to calculate the vertical values
            verticalScale  = query(myScope,'WFMOUTPRE:YMULT?');
            verticalScale = str2double(verticalScale);

            % Request 8 bit binary data on the CURVE query
            fprintf(myScope, 'DATA:ENCDG RIBINARY;WIDTH 1');

            while value == true

            fprintf(myScope, 'WAVFrm?');
            waveform = binblockread(myScope,'int8');

            YData  = (waveform-yOffset).*verticalScale + vertOffset;    

            app.YDataEditField.Value = YData(100);

            XData = (xIncr.*(1:length(YData))) - xIncr;

            app.XDataEditField.Value = XData(100);

            timeBase = str2double(query(myScope, 'HORizontal:SCAle?'));
            app.XScaleEditField.Value = timeBase;

            voltsPerDiv = str2double(query(myScope,'CH1:SCAle?'));         
            app.YScaleEditField.Value = voltsPerDiv;

            xlim(app.UIAxes, [0 timeBase*15]);
            ylim(app.UIAxes, [0 10*voltsPerDiv]);

            plot(app.UIAxes, XData, YData); 

            app.UIAxes.XGrid = 'on';
            app.UIAxes.YGrid = 'on';

            drawnow

            if value == false
                break

            end

            end

            plot(app.UIAxes, 0);
  end

[Jan]

Without seeing the code it is impossible to guess the source of problems.

[miki90]

I've put a code now. Sorry for the long code, I don't know how to put a code to have a slider.