Extech thermo hygrometer with data logging extech sdl500 the extech sdl500 thermo hygrometer data logger records data on an sd card in microsoft excel reg format for easy transfer to a pc for analysis the user can manually store 99 readings or set the logger to automatically store up to 20m samples with date and time stamp at a user selected sample rate it measures relative humidity temperature dew point and wet bulb temperture supplied with 6 x aa batteries sd card carrying case and