Chris Dennis wrote: > I've noticed that, of the four holes in the middle of the instrument, > three look shiny and reflective when I peer into them and the fourth is > dark. The dark one is at the north-east position when the USB cable is > 'north'. Is that normal? That's normal. There's room in the design for a fourth filter, but it's not used. > I've tried prising the case apart to have a look inside, but so far it has > resisted my efforts. I'd imagine that there are two screws underneath the label. Graeme Gill.