I bought a digital thermometer with min/max from Walmart for $5, but the problem was the temperature would rise quite a bit (above 40F) if the door was left ope

I bought a digital thermometer with min/max from Walmart for $5, but the problem was the temperature would rise quite a bit (above 40F) if the door was left open even for ~10-30 seconds, so it was hard to use the "max" temperature reading. It would have been more handy if the thermometer's min and max responded more slowly to reject these short fluctuations.