Cheap digital thermometers

[Fornax]

Hi All,

Earlier this year I build an HRV but I had no good way to measure it's efficiency. To accurately measure that I need exact readings from 4 spots at the same time but I only had 2 simple thermometers.

After looking around I decided to order some cheap digital ones from a far country (dx.com). Since they were fairly cheap with free P&P I decided to order 10 so I could surely find a set of 4 that would agree with eachother.

To my pleasant surprise the package was delivered to my door in only 9 days.

After unpackaging everything and inserting the batteries (which gave me a good feel for the cheap buildquality of the items) I build a contraption to see if the 10 thermometers agree with eachother.
With some foam I put the sensors thightly stuck in a piece of aluminium rail, put it all in a nondraughty place and let it sit for an hour.

I found 2 sets of 4 that nicely agree with eachother which will let me make accurate calculations on my HRV, see attached thumbnails.

Although the 10 thermometers do agree with eachother the actual temperature measured with 2 known-good ones (also visible in the images) is a full 2 degrees centigrade lower...