Stay within the ASTM F2170 Standard of calibration with replacement reusable Smart Sensors for your Rapid RH 4.0 Reusable Smart Sensor Kit. Reusable Smart Sensor 5-pack: $425 5 ea. Rapid RH 4.0 Reusable Smart Sensors 5 ea. EasyCare CalChecks at 75% Relative Humidity 10 ea. Sleeve Extensions 5 ea. Protective Caps 1 ea. Certificate of Calibration 1 ea. Floor Map