The Testo 171 is a high performance logger series with built-in sensors for Temperature (NTC) and / or Relative Humidity. This series has a large memory, accurate and comes in a rugged housing made of anodized aluminum.
 

Testo 171 Series	Testo 171-2	Testo 171-3	Testo 171-6
Product Picture
Temperature measuring range	-20 to 70ºC (-4 to 158ºF)	-25 to 50ºC (-14 to 122ºF)	-50 to 120ºC (-58 to 248ºF)
Sensor	NTC	NTC	NTC
Humidity Range	0 to 100%	0 to 100%	0 to 100%
Measuring Rate	2 s to 24 h (freely selectable)	2 s to 24 h (freely selectable)	2 s to 24 h (freely selectable)
Memory Capacity	55,000 measured values	55,000 measured values	55,000 measured values
Protection Class	IP65	IP65	IP65
Housing	Aluminum, anodized	Aluminum, anodized	Aluminum, anodized
Dimensions	5.16 x 2.68 x 1.02"	5.16 x 2.68 x 1.02"	5.16 x 2.68 x 1.02"
Software	Requires Windows 3.0 or higher	Requires Windows 3.0 or higher	Requires Windows 3.0 or higher
Warranty	2 years	2 years	2 years

Note: The above Loggers of the 171 Series are all measuring Temperature and RH. Other 171 loggers measure exclusively temperature. Please see the temperature section for details.