The Serviceman today needs an instrument that is reliable, durable and accurate, has usable functions and probes for measuring refrigeration and air-conditioning systems, and is reasonably priced. The Weiss DT51A and DT52A offer such a product for temperature measurement.
The DT51A-1 is a type K thermocouple based single probe thermometer with a range of -50/1999°F, resolution switch (0.1°F or 1°F), Data Hold feature, Max Memory, °F or °C switch and includes a general use probe.
The DT52A-4 is also type K thermocouple with two probe inputs that offer the differential feature required in refrigeration and air-conditioning service. Includes two velcro probes with the sensor built in, plus a bead probe and general probe with handle in an ABS carrying case.

SPECIFICATIONS ELECTRICAL Measurement Range: -50 to 1300°C -50 to 1999°F Resolution: 0.1° or 1° ENVIRONMENTAL Ambient Operating Range: 0 to 50°C 32 to 122°F Storage Temperature: -10 to 60°C -14 to 140°F Humidty: 0% to 90% (0 to 35°C) 0% to 70% (35 to 50°C) ACCURACY For single-thermocouple measurements. For T1-T2 Measurements accuracy is: ±(0.3% of T1-T2 reading +2°C) ±(0.3% of T1-T2 reading +3°F) GENERAL Weight: 206 GM (7.2 oz) Dimension: 5.31"L x 2.83"W x 1.22"H (135x72x31mm) Battery: Standard 9V battery (NEDA 1604,6F22,or 006P) Battery life: Approx.150 hours. Display: (4) 1/2" digit liquid crystal display, 14mm high LCD. Yellow Grip Sleeve: Included. Data Hold Feature - Max Hold Feature Output Jack: For temperature recording or computer interface. Instruction manual: Included.