It's not a separate opening or anything, just a little 'spot' in the LCD panel that has the digital readout. Looks almost like a decimal point at first, but looking closer you'll see it pulse on/off and it's situated a little bit lower than the digits. Have fun...
daestrom P.S. NiMo did our gas-meters as well, but kept the mechanical readout. Just installed some sort of 'extender' on the readout with a radio/modem behind it.