I built the Thermometer project using the sensor in my kit. Trouble was it was reading the wrong voltage. I would read A/D value of 350 or about .28 VDC, but it should have read 875 or about .7 VDC. The voltage checked correct with an external voltmeter. I tried to read the voltage while my external voltmeter was connected and guess what ?, it read 875 as it should as long as the external meter was connected.
I think this is because the external voltmeter added a tiny bit of capacitance which fixes a typical problem with A/D converters called aliasing. Many A/D chips call for a small filter capacitor on their inputs to prevent this problem.
I added a .01uF cap to the input pin and it works great every time. Called a anti-aliasing capacitor.
Good practice would be to add a small cap to all A/D inputs or even an opp amp buffer with a small cap.