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 thermocouplewith two probe inputs that offer the differential feature required in refrigerationand 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.