The Exo Terra Digital Hygrometer with minimum and maximum air humidity memory is an electronic precision instrument for monitoring the terrariums relative air humidity levels. Two hygrometers are recommended in large terrariums to precisely monitor the humidity gradients. This instrument has a unique remote sensor with a minimum and maximum temperature memory. It fits the Exo Terra Compact top and dual top canopies and comes with batteries included. Install an Exo Terra LED Hygrometer into your terrarium and be in control of your reptiles environment.