What they are, V blocks. I haven't tested them for quality as I don't have an equalizer or other concurrency checking hardware, so don't expect great accuracy.
๐ฌ๏ธ Advanced 3-in-1 Indoor Air Quality Monitor with CO2/RH/Temp Data Logging and Audible Alarm - NDIR Sensor Technology
8 Review
๐ง UEi Test Instruments DAFM3B Digital Multimeter
6 Review
๐ก๏ธ Continuous Temperature Monitoring with Relative Humidity Integration
4 Review
๐ Enhanced Precision with Backlit Professional Manometer for Differential Ventilation
6 Review