I know this is an old thread but it is worth once more round the Block,,
I tested mine with a analogue thermometer and a Laser and I knew mine was close so after reading a lot of the posts on the forum about the temperature difference's people have had I decided that I would recheck it and I was right it is very close because I put a Digital thermometer in there as well and it reacts faster than the ARB's thermometer and I had set the fridge to 05*c and when you leave it to settle the temp can drop another 6 or 7*c degrees the digital thermometer said -1.9*c and then -2*c and when the fridge was flashing backwards and forwards from -2 to -3 the digital thermometer was reading -2.6*c and when it changed to -2.7 to -2.8*c the ARB was reading -3*c and when the Digital thermometer was reading -3.0 so was the ARB and the Laser Confirmed that it is accurate to within 0.1*c So I guess I got lucky with this one, Because I have not had to Calibrate my ARB at all.
Thank you to everyone who posted the info about this, you've been a Great help.