I recently purchased a TEMPer2 Device from an ebay reseller at http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&item=300619217719 . After receiving the device I shortly tested it and found it reporting normal ambient room temperature just fine.

Being advertised as capable of measuring -40°C to 120°C I finally came to set it up as a combined indoor and outdoor sensor last week. Sadly I had to notice that it failed to report negative °C values correctly.

As soon as the sensor starts reporting temperatures below 0°C it jumps up to 254°C.

http://i.imgur.com/yJ5TO.png

Sadly it only came to my mind after sending the TEMPer2 device back to the vendor. It's a simple error in binary interpretion. The reading seems to be interpreted as unsigned character instead of a signed character, which would explain a reading of 254°C instead of -2°C.

11111110 unsigned char -> 254
11111110 signed char -> -2

The faulty readings happened with TEMPer2 23.1 http://www.pcsensor.com/uploadFile/APPsoftware/TEMPer%20V23.1.zip and 23.3 http://www.pcsensor.com/uploadFile/APPsoftware/TEMPer%20V23.3.zip downloaded from your site.