Voltcraft ht 100 professional digital pen thermo hygrometer voltcraft ht 100 p the voltcraft ht 100 is a compact professional digital pen thermo hygrometer that is ideal for mobile use the metal clip ensures a secure attachment the ht 100 is powered by 1x aaa battery the flat battery cover allows for a vertical measuring position the dual display shows the values for temperature and relative humidity simultaneously p voltcraft ht 100 digital pen thermo hygrometer