In accordance with ASTM F2170, you should use:
- 3 Smart Sensors (aka probes, sensor barrels) must be used for first 1,000 square feet.
- 1 Smart Sensor for every additional 1,000 square feet.
- If your slab is 1,200 square feet then you would need 4 sensors.

Please visit 10 Guidelines for ASTM F2170 Compliance and Video 16 – Best Locations to Place Relative Humidity Probes for more information.