Amazon calculates a product’s star ratings using a machine learned model instead of a raw data average. The machine learned model takes into account factors including: the age of a review, helpfulness votes by customers and whether the reviews are from verified purchases.
It is a very convenient tool to charge your mobilephone. Leave your mobilephone touch on the mechine, don’t need the line. It is very convenient when you are out of home without line. It seems to charge about three times for mobilephone.