Excellent. A must for all and especially landlords and tenants. We use them in conjunction with humidistat extractors, dehumidifiers and PIV. Locate on the wall in problem areas and potential cold spots. Informs everyone about air quality in the property and what is needed to manage the environment for health, comfort and to avoid damage. The 5 coloured dial makes it intuitively easy to understand. Max and minimum reading also provides useful information.