Hi Rashmi, This subject is open to different interputations throughout the UK, we believe in giving the customers what they want, to give them peace of mind. However you know who we go too, for advice from time to time, and I will send you said info privately, you should map in core with 200ml of ordinary "tapwater", some add Glycerol such as the NBS, which is optional, the reason for water and not air, is the temperature fluctuations are more accurate, and when you have an intrusion (door opening) the data is then recorded in seconds, so you can see the temperature rising the longer you leave the door open, we have also found when air temps have been used in some fridges that are borderline, you can have shelves taken out of service for cold or hot spots, using water can sometimes bring them back into use. Cheers ABBWalker.