This document provides a user guide for Extech Instrument's datalogging instrumentation and software. It covers the hardware and software operation of Model 42275 Temperature and Humidity Datalogging Module and SW276 WindowsTM Software. It also covers the software and some hardware operation of Model 42270 Temperature and Humidity Datalogging Module, with a separate manual provided for detailed hardware operation. The datalogging modules can be used to monitor the temperature of greenhouses, warehouses, food transports, aircraft cabins, refrigerated trucks, containers, museums, and HVAC equipment. The modules can store 16,000 readings that can be transferred to PC or directly printed using the Model 42276 Programmer/Printer.