The TR-77Ui from TandD Corp., Saratoga Springs, NY, is a compact 2 by 3 in. logger that operates from a single AA battery and measures humidity from 0%–99% RH and temperature from –30°C to 80°C. Accuracy is ±2.5% (RH, uncalibrated). Features include a 20 s humidity time constant, memory capacity for 16,000 readings in one-time or endless recording mode, and data transfer via USB. A built-in adjustment function lets you enter calibration factors into the logger.