Display
DISPLAY: 
COMM: Appears when the device is connected to a computer
MIN/MAX/AVG: Minimum, maximum or average value of the stored data (function available only in LOG mode).
FULL: Appears when storage is full
LOG: Appears when the logging function is active
Battery Symbol: Appears when the battery is low
°C/°F: Temperature
%RH: Relative humidity (BL-1D, HL-1D)
hPa: Pressure (BL-1D)
DP °C/°F: Dewpoint (BL-1D)
Hi, Lo: Appears when temperature or humidity exceed the High Alarm or Low Alarm threshold
START / STOP Button
Press the button once to switch the device on or off (the device cannot be switched off in LOG mode). To start or stop data logging, press the START/STOP button and hold it down until "LOG" appears on the display, or program the desired logging time using HygroSoft.
MODE Button
Every 5 seconds (default value), or when the MODE button is pressed, the display toggles between "Humidity & Temperature" and "Pressure & Dewpoint". In LOG mode, press and hold down to display the MIN/MAX/ AVG of the stored data.
HL-1D / TL-1D:
In LOG mode, press the button for a moment to display the MIN/MAX/AVG of the stored data.
BL-1D:
LED Status Indicator
In Log mode, the right-hand LED flashes green every 5 seconds. When the alarm threshold has been exceeded, or if the battery is low, the left-hand LED flashes red every 5 seconds.
2 LEDs; right-hand LED flashes green during data logging, left-hand LED flashes red when thresholds are exceeded or the battery is low.