How do I get the right readings from a NXT magnetic sensor?

Hi, I'm currently working on a project that involves matlab being able to continuously get readings from a "HiTechnic magnetic sensor". But apparently matlab doesn't fully support that specific sensor, so my proffesor said that I should try and use one of these sensors code in it's place: https://wiki.qut.edu.au/display/cyphy/Device+Types He also said that I should try and use this code to try and get it to work:

reading = b.inputReadSI(0,Device.Port1,Device.X)'

But no matter which one I try it either doesn't work or give the same "50.6716" value no matter how strong the surronding magnetic field is. Does anyone know how I should fix this. The code I'm currently working with is:

b = Brick('ioType','usb');
tic;
while (toc <= 30) % Runs for 30 sec'
    pause(0.5);
reading = b.inputReadSI(0,Device.Port1,Device.X) %The part named "Device.X" is where I test the different sensors.
disp(reading);
end